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Ta3N5 Nanotube Arrays for Visible Light Water Photoelectrolysis
Abstract
Tantalum nitride (Ta3N5) has a band gap of approximately 2.07 eV, suitable for collecting more than 45% of the incident solar spectrum energy. We describe a simple method for scale fabrication of highly oriented Ta3N5 nanotube array films, by anodization of tantalum foil to achieve vertically oriented tantalum oxide nanotube arrays followed by a 700 degrees C ammonia anneal for sample crystallization and nitridation. The thin walled amorphous nanotube array structure enables transformation from tantalum oxide to Ta3N5 to occur at relatively low temperatures, while high-temperature annealing related structural aggregation that commonly occurs in particle films is avoided. In 1 M KOH solution, under AM 1.5 illumination with 0.5 V dc bias typical sample (nanotube length approximately 240 nm, wall thickness approximately 7 nm) visible light incident photon conversion efficiencies (IPCE) as high as 5.3% were obtained. The enhanced visible light activity in combination with the ordered one-dimensional nanoarchitecture makes Ta3N5 nanotube arrays films a promising candidate for visible light water photoelectrolysis.
... Since first PEC demonstration with TiO2 photoelectrode [4][5][6][7][8] different nano structural materials have been studied extensively. In recent years, photo electrodes made from Ta3N5 has been demonstrated for PEC water splitting as thin films and particles [11][12][13], vertically aligned Ta3N5 nanorod photoelectrode was found to yield efficient photocurrent density compared to planer Ta3N5 [14]. ...
... As shown in figure that present Mott-Schottky plot for ZnO BNW at various frequencies, the positive slope indicates ZnO BNW:N as n-type semiconductor with electron conduction. For reaction of water splitting to proceed, Vfb of photo-anode used in PEC should be more cathodic than the reduction potential of hydrogen (Eh) at used electrolyte [14]. Eh varies as a function of pH value and can be quantified by the equation Eh = 0 -0.059(pH) it was found to be = (-0.42775) ...
... In Fig. 7 the calculated results, using above equation, plotted versus applied potential show the maximum efficiency value of 0.3%, that obtained at an applied potential +0.8 V. This result is higher than the hydrogen efficiency reported before from undoped vertically aligned ZnO nanowires and from that doped with nitrogen by thermal annealing [14], undoped TiO2 nanowires [21], ZnO nano-coral [22], and ZnO:N films [20,23] asphotoanodes. ...
Photoanode of ZnO branched nanowires, BNW, doped with nitrogen was fabricated to be used in photochemical cell for hydrogen generation from water splitting process. ZnO BNW was first synthesized by hydrothermal method. Followed by time-control DC glow discharge plasma treatment, to optimize nitrogen doping into nanowire structure. Via X-ray photoelectron spectroscopy (XPS) results, BNW with up to 25% atomic ratio of N to Zn was achieved by plasma treatment. XPS studies confirm nitrogen distribution into ZnO BNW as N substitution at O sites of ZnO nanowires and as well screened molecular nitrogen. Modified BNW electronic structure reflected into flat band potential that increased negatively with N contain into BNW. Photo-electrochemical studies were demonstrated upon dark and illumination at various power densities. Increasing N contain into BNW leads to increase photocurrent on PEC (Photo-electrochemical cell). Hydrogen generation from water splitting efficiency of 0.3% was achieved for BNW doped with 25% N.
... Since first PEC demonstration with TiO2 photoelectrode [4][5][6][7][8] different nano structural materials have been studied extensively. In recent years, photo electrodes made from Ta3N5 has been demonstrated for PEC water splitting as thin films and particles [11][12][13], vertically aligned Ta3N5 nanorod photoelectrode was found to yield efficient photocurrent density compared to planer Ta3N5 [14]. ...
... As shown in figure that present Mott-Schottky plot for ZnO BNW at various frequencies, the positive slope indicates ZnO BNW:N as n-type semiconductor with electron conduction. For reaction of water splitting to proceed, Vfb of photo-anode used in PEC should be more cathodic than the reduction potential of hydrogen (Eh) at used electrolyte [14]. Eh varies as a function of pH value and can be quantified by the equation Eh = 0 -0.059(pH) it was found to be = (-0.42775) ...
... In Fig. 7 the calculated results, using above equation, plotted versus applied potential show the maximum efficiency value of 0.3%, that obtained at an applied potential +0.8 V. This result is higher than the hydrogen efficiency reported before from undoped vertically aligned ZnO nanowires and from that doped with nitrogen by thermal annealing [14], undoped TiO2 nanowires [21], ZnO nano-coral [22], and ZnO:N films [20,23] asphotoanodes. ...
... Other oxide-based photoelectrodes, such as La-doped NaTaO 3 [18] and Rh-doped SrTiO 3 [19], show reasonable quantum efficiencies (QEs) in the presence of UV light, and have been utilized as H 2 evolution photocatalysts in visible-light irradiation. Oxynitride-based photoanodes offer an alternative to oxide-based anodes for visible-light absorption to produce H 2 and O 2 from water at a stoichiometric ratio [17,[20][21][22][23][24][25]. In these materials, atomic nitrogen is introduced into the oxygen sites, and it shifts the VB edge potentials to the more negative region via the hybridization of N 2p and O 2p orbitals. ...
... In these materials, atomic nitrogen is introduced into the oxygen sites, and it shifts the VB edge potentials to the more negative region via the hybridization of N 2p and O 2p orbitals. Domen et al. demonstrated TaON/co-catalyst-based photoanodes with an incident photon-to-electron conversion efficiency (IPCE) of 76% at 400 nm for water oxidation at a minimal or no external applied bias [20][21][22][23][24][25][26]. Since then, oxynitrides, such as LaTiO 2 N [22], SrNbO 2 N [27,28], BaNbO 2 N [29], among other materials, have been similarly developed as photoanodes [30][31][32][33][34][35]. ...
... Currently, significant research is underway to develop the smaller band-gap photoanodes with a BG of <2 eV (equivalent to 600 nm in the visible absorption spectrum) to oxidize water with the application of minimal bias [33]. Several such photoanodes have been developed, e.g., BaNbO 2 N [21], CoO x /LaTiO 2 N [22], and BaZrO 3 /BaTaO 2 N [33], which have been found to utilize the absorption of visible-light in addition to appropriate sacrificial reagents. SrNbO 2 N-based photoanodes (BG < 2 eV), function as water-oxidation catalysts with the support of a co-catalyst in visible-light illuminations [27,28,34]. ...
Photoanodes fabricated by the electrophoretic deposition of a thermally prepared zinc tantalum oxynitride (ZnTaO 2 N) catalyst onto indium tin oxide (ITO) substrates show photoactivation for the oxygen evolution reaction (OER) in alkaline solutions. The photoactivity of the OER is further boosted by the photodeposition of cobalt phosphate (CoPi) layers onto the surface of the ZnTaO 2 N photoanodes. Structural, morphological, and photoelectrochemical (PEC) properties of the modified ZnTaO 2 N photoanodes are studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet visible (UV−Vis) diffuse reflectance spectroscopy, and electrochemical techniques. The presence of the CoPi layer significantly improved the PEC performance of water oxidation in an alkaline sulphate solution. The photocurrent-voltage behavior of the CoPi-modified ZnTaO 2 N anodes was improved, with the influence being more prominent at lower oxidation potentials. A stable photocurrent density of about 2.3 mA·cm −2 at 1.23 V vs. RHE was attained upon visible light illumination. Relative to the ZnTaO 2 N photoanodes, an almost threefold photocurrent increase was achieved at the CoPi/ZnTaO 2 N photoelectrode. Perovskite-based oxynitrides are modified using an oxygen-evolution co-catalyst of CoPi, and provide a new dimension for enhancing the photoactivity of oxygen evolution in solar-assisted water-splitting reactions.
... The corrosion potential of the 304 stainless steel was initially determined to be approximately −0.17 V in 3.5 wt% NaCl solution by potentiodynamic polarization measurements. The unmodified Ta 3 N 5 also has photocatalytic activity [23,24,39] and theoretically should generate some degree of protective potential. However, the actual results in Figure 6a show that the potential of the unmodified Ta 3 N 5 could only reach to −0.12 V after the first illumination (300 s). ...
... The corrosion potential of the 304 stainless steel was initially determined to be approximately −0.17 V in 3.5 wt% NaCl solution by potentiodynamic polarization measurements. The unmodified Ta3N5 also has photocatalytic activity [23,24,39] and theoretically should generate some degree of protective potential. However, the actual results in Figure 6a show that the potential of the unmodified Ta3N5 could only reach to −0.12 V after the first illumination (300 s). ...
In this work, CoPi and Co(OH)2 nanoparticles were deposited on the surface of Ta3N5 nanorod-arrays to yield a novel broad-spectrum response photocatalytic material for 304 stainless steel photocatalytic cathodic protection. The Ta3N5 nanorod-arrays were prepared by vapor-phase hydrothermal (VPH) and nitriding processes and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-Vis spectroscopy, respectively, to obtain morphologies, crystal structures, surface compositions, and light response range. In order to analyze the performance improvement mechanism of CoPi/Co(OH)2 on Ta3N5 nanorod-arrays, the electrochemical behavior of modified and unmodified Ta3N5 was obtained by measuring the open circuit potential and photocurrent in 3.5 wt% NaCl solution. The results revealed that the modified Ta3N5 material better protects 304 stainless steel at protection potentials reaching −0.45 V.
... Among semiconductor photocatalysts, Ta 3 N 5 with a narrow band gap of approximately 2.1 eV can absorb and utilize a large fraction of visible light up to 600 nm, and Ta 3 N 5 nanomaterials [26][27][28][29] and/or films [30][31][32][33][34][35] have been prepared as visible-light-driven (VLD) photocatalysts. Herein, by using Ta 3 N 5 as a model semiconductor, we report the design and preparation of Ta 3 N 5 -Pt nonwoven cloth that is composed of nanofibers constructed from Ta 3 N 5 nanoparticles, hierarchical nanopores and Pt nanoparticles. ...
... The spectrum of Ta 2 O 5 cloth is similar to what has been reported previously for Ta 2 O 5 samples 26 , and it exhibits a short-wavelength absorption edge at approximately 330 nm. Importantly, Ta 3 N 5 cloth shows a large red shift from 330 to 600 nm, due to the band gap narrowing caused by the substitution of N for O atoms 36 , which agrees well with the reported value for the bandgap (Eg < 2.1 eV) of Ta 3 N 5 samples 26,30 . Furthermore, after the decoration of Pt, no obvious change of absorption spectrum has been observed. ...
... Photo-electrochemical water splitting for hydrogen generation has recently attracted increasing attentions owing to its store solar energy into chemical energy [1][2][3][4][5][6] , revealing the possibility to replace current fossil fuel 1,2,4 . Materials served as photoelectrodes (PEs) for efficient water splitting should fulfill the following requirements: (i) a good match between the absorption wavelength and the solar spectrum to satisfy the energetic for electrolysis; (ii) a high quantum yield; (iii) a correct energy band edge straddling water's redox potential 2 . ...
... BiVO 4 -based PEs have to work with the assistant of promoter under a high applied external bias 12,13 . The surface of Ta 3 N 5 photoelectrodes is easy to be oxidized, which is not stable enough for future applications 3 . Very recently, III-nitride semiconductors are considered as one of the most suitable candidate materials for solar hydrogen production [14][15][16][17] , especially the indium gallium nitride (InGaN) alloys, which have an adjustable direct band gap perfectly matching solar spectrum, a high carrier mobility and excellent chemical stability [18][19][20] . ...
The photoelectrodes based on III-nitride semiconductors with high energy conversion efficiency especially for those self-driven ones are greatly desirable for hydrogen generation. In this study, highly ordered InGaN/GaN multiple-quantum-well nanorod-based photoelectrodes have been fabricated by a soft UV-curing nano-imprint lithography and a top-down etching technique, which improve the incident photon conversion efficiency (IPCE) from 16% (planar structure) to 42% (@ wavelength = 400 nm). More significantly, the turn-on voltage is reduced low to −0.6 V, which indicates the possibility of achieving self-driven. Furthermore, SiO2/Si3N4 dielectric distributed Bragg reflectors are employed to further improve the IPCE up to 60%. And the photocurrent (@ 1.1 V) is enhanced from 0.37 mA/cm2 (original planar structure) to 1.5 mA/cm2. These improvements may accelerate the possible applications for hydrogen generation with high energy-efficiency.
... 18 In the case of Ta 3 N 5 , there have been few reports on the syntheses of NTs applied in photoelectrochemical water splitting. 2,10 Thus, the synthesis of single-crystal-like or preferentially oriented pristine Ta 3 N 5 NTs is highly desirable. ...
... Similar results can be confirmed from selected area electron diffraction patterns ( Figure S6). The inset of Figure 6d presents the simulation of electron diffraction patterns viewed along the [1][2][3][4][5][6][7][8][9][10] zone axis, which is in agreement with the experimental distances, and the (110) can be observed clearly; ...
... Photo electrodes made from Ta3N5 have been demonstrated for PEC water splitting as thin films and particles. [11][12][13]. Developing of vertically aligned Ta3N5 nanorod photoelectrode yielded efficient photocurrent density compared to planer Ta3 N5 [14]. ZNO nanostructured was developed and doped with N to improve its light absorption in the visible region, and photo to hydrogen conversation efficiency. ...
... In general, tantalum (oxy)nitride-based materials are synthesized from tantalum-based oxide precursors via nitridation at high tem- perature with ammonia (NH 3 ) gas as the nitrogen source [14]. For Ta 3 N 5 and TaON, many preparation methods have been reported to synthesize Ta 2 O 5 precursors, including reverse homogeneous precip- itation reactive sputtering, atomic layer deposition, and vapor phase hydrothermal processes [56][57][58][59][60][61]. For the tantalum-based oxynitride perovskite, a solid-state reaction is normally applied to synthesize the oxide precursors. ...
Photocatalytic water splitting, which directly converts solar energy into hydrogen, is one of the most desirable solar-energy-conversion approaches. The ultimate target of photocatalysis is to explore efficient and stable photocatalysts for solar water splitting. Tantalum (oxy)nitride-based materials are a class of the most promising photocatalysts for solar water splitting because of their narrow bandgaps and sufficient band energy potentials for water splitting. Tantalum (oxy)nitride-based photocatalysts have experienced intensive exploration, and encouraging progress has been achieved over the past years. However, the solar-to-hydrogen (STH) conversion efficiency is still very far from its theoretical value. The question of how to better design these materials in order to further improve their water-splitting capability is of interest and importance. This review summarizes the development of tantalum (oxy)nitride-based photocatalysts for solar water spitting. Special interest is paid to important strategies for improving photocatalytic water-splitting efficiency. This paper also proposes future trends to explore in the research area of tantalum-based narrow bandgap photocatalysts for solar water splitting.
... Tantalum has excellent chemical properties, which has extremely high corrosive. Sputtering tantalum film of sapphire optical fiber is shown in the Figure 2, tantalum film membrane layer of SEM figure is shown in the Figure 3. See from the figure that the film surface is smooth, no cracks and other defects [1][2][3] . In the air, tantalum oxidation begins from 300～325 ℃ , when the temperature is higher than550 ℃ , oxidation rate increased significantly, generate Ta 2 O 5 . ...
In order to realize the transient high temperature measurement in the harsh environment and narrow space, a sapphire fiber tantalum (melting point 2997 ℃)-zirconia (melting point 2715 ℃) thin film black body cavity transient high temperature sensor is developed by the sputtering and plasma spraying technology. Constant high temperature static sensitivity calibration device, which is composed of three water electrolysis oxyhydrogen flame guns, and dynamic characteristic calibration device with high power and high frequency modulated CO2 laser pulse as step excitation source are designed. The measured results show that, when the temperature of constant temperature area of the static sensitivity calibration device is 1721 ℃ and the impact resistance of the sensor is up to above 50 MPa, the temperature measured by the sensor is 2802 ℃. When the CO2 laser pulse is used as a high temperature step input signal at 1500 ℃, the time constant measured by the sensor is μs order of magnitude.
... Therefore, its CB and VB positions are suitable for water splitting. Meanwhile, Ta 3 N 5 has a theoretical maximum solar spectrum photoconversion efficiency of 15.9% [96,97]. Owing to the above merits, Ta 3 N 5 is a good candidate as a photocatalyst under visible light irradiation [98][99][100][101]. ...
Photocatalysis has received much attention as it is considered one of the potential solutions for solar energy conversion and counteracting environmental degradation. In order to promote the research work of the field and meet the requirements of practical applications, it is necessary to develop high efficiency visible-light-driven photocatalysts, especially the red semiconductor photocatalysts. This review aims to sum up the progress recently made in this field, concentrating on the scientific and technological possibilities offered by three kinds of red semiconductor photocatalysts for water splitting, organic contaminant decomposition, and CO
... nanorods and nanotubes) have the advantages of improving absorbance, and promoting the transport and separation of photoexcited charge carriers [5][6][7][8][9]. Recently, photoelectrodes of Ta 3 N 5 nanotube [10][11][12] and nanorod [13][14][15][16] arrays have been fabricated and showed enhanced PEC activity, demonstrating the high potential of such 1D Ta 3 N 5 nanostructures. ...
Conversion of solar energy into H 2 by photoelectrochemical (PEC) water splitting is recognized as an ideal way to address the growing energy crisis and environmental issues. In a typical PEC cell, the construction of photoanodes is crucial to guarantee the high efficiency and stability of PEC reactions, which fundamentally rely on rationally designed semiconductors (as the active materials) and substrates (as the current collectors). In this review work, we start with a brief introduction of the roles of substrates in the PEC process. Then, we provide a systematic overview of representative strategies for the controlled fabrication of photoanodes on rationally designed substrates, including conductive glass, metal, sapphire, silicon, silicon carbide, and flexible substrates. Finally, some prospects concerning the challenges and research directions in this area are proposed.
The trade-off between light absorption and carrier transport in semiconductor thin film photoelectrodes is a major limiting factor of their solar-to-hydrogen efficiency for photoelectrochemical water splitting. Herein, we develop a heterogeneous doping strategy that combines surface doping with bulk gradient doping to decouple light absorption and carrier transport in a thin film photoelectrode. Taking La and Mg doped Ta3N5 thin film photoanode as an example, enhanced light absorption is achieved by surface La doping through alleviating anisotropic optical absorption, while efficient carrier transport in the bulk is maintained by the gradient band structure induced by gradient Mg doping. Moreover, the homojunction formed between the La-doped layer and the gradient Mg-doped layer further promotes charge separation. As a result, the heterogeneously doped photoanode yields a half-cell solar-to-hydrogen conversion efficiency of 4.07%, which establishes Ta3N5 as a leading performer among visible‐light‐responsive photoanodes. The heterogeneous doping strategy could be extended to other semiconductor thin film light absorbers to break performance trade-offs by decoupling light absorption and carrier transport.
Semiconductors and the associated methodologies applied to electrochemistry have recently grown as an emerging field in energy materials and technologies. Fuel cells have been developed in line with traditional electrochemistry employing three basic functional components: anode, electrolyte and cathode. The electrolyte is a key component to the device performance by providing an ionic charge flow pathway between the anode and cathode but preventing electron conduction. By contrast, semiconductors and the derived heterostructures with electronic (hole) conducting materials have been strongly developed with much better ionic conductors instead of a conventional ionic electrolyte for novel fuel cells. Energy band structures and alignments, band‐bending and built‐in‐field are all important parameters in this context to accomplish the necessary fuel cell functionalities. This chapter extends widely the semiconductor‐based electrochemical energy conversion and storage technologies, describing their fundamentals and working principles, with an intention to advance the understanding of the semiconductors and energy bands role in electrochemical devices of energy conversion and storage, as well as applications for emerging demands, widely involving in energy applications, such as photo catalysis/water splitting; battery and solar cell etc. It provides new ideas and new solutions to the problems beyond the conventional electrochemistry and presents new inter‐disciplinary approaches to develop clean energy conversion and storage technologies.
Photovoltaics (PVs) market is currently dominated by mono- and multi-crystalline silicon, which has formed the basis of PV technology. However, breakthroughs in silicon solar cells photovoltaic energy conversion efficiency seem to be unlikely, and although further development in solar cells design might further increase their efficiency, cost projections are still not favorable. Hence, other materials and structures have been developed or are under development. In this chapter, we will examine different solutions, including thin film, heterojunction structures, organic materials, and hybrid (organic-inorganic) solar cells as possible alternatives to conventional crystalline PV devices. Furthermore, optoelectronic materials' properties and solar cells configurations will be analyzed with respect to various PV applications.
A ZnO branched-nanowire (BNW) photoanode was doped with N for use in a photoelectrochemical cell (PEC) to generate H2 from water splitting. First, ZnO BNWs were synthesized by chemical bath deposition method. Two experimental methods were used for N-doping: the time-controlled direct-current glow discharge plasma (DCGDP) and the DC magnetron plasma (DCMP) methods, to optimize N-doping of the NW structure. X-ray photoelectron spectroscopy (XPS) provided the N distribution and atomic percentage in the BNWs. The XPS results confirmed that N distribution into ZnO BNWs occurred by N substitution of O sites in the ZnO structure and through well-screened molecular N2. The morphologies and structures of the fabricated nanostructures were investigated by field-emission scanning electron microscopy and X-ray diffraction respectively. The photoanode performance was demonstrated in photoelectrochemical studies at various power densities under both dark and illuminated conditions. Increasing the N amount in the ZnO BNWs increased the photocurrent in the PEC.
Ta3N5-Au heterojunction was prepared via a facile solvothermal precipitation-nitridation-wet impregnation method. Ta3N5-Au consisted of Ta3N5 microspheres (diameters: 1–2.5 μm) and Au nanoparticles (size: ∼3.5 nm). Ta3N5 microsphere was composed of nanorods (diameter: 20–30 nm; length: 400–500 nm), and Au nanoparticles were well-dispersed on the surface of Ta3N5 nanorods. Photocatalytic performances of as-prepared catalysts were evaluated by the degradation of MB, RhB or 4-CP under visible light irradiation (λ > 400 nm), flower-like Ta3N5-Au exhibited higher photocatalytic activity than flower-like Ta3N5, bulk Ta3N5 or Ta3N5-Au. The enhanced photocatalytic activity of Ta3N5-Au could be attributed to the synergistic effect of high surface area and efficient separation of photogenerated charge carriers. The photogenerated holes (h⁺) and superoxide radical anions (O2⁻) were found to be the leading active species responsible for the degradation of RhB dye. The cycling experiments demonstrated that flower-like Ta3N5-Au had good recyclability.
Among various material nanoarchitectures, the nanotube geometry has received incredible attention due to the unique properties provided by its high surface area as well as nanoscale wall thickness and the availability of a variety of techniques to fabricate them. Since the beginning of this century, anodization has emerged as one of the most effective techniques for the fabrication of functional oxide nanotubes. Oxide nanotubes of a number of metals and alloys have been developed using this versatile technique. We review here the research activities on anodic nanotubes of various binary, ternary, and multinary materials and their selected applications.
In this study, we conceptually develop and thermodynamically analyze a new continuous-type hybrid system for hydrogen production which photoelectrochemically splits water and performs chloralkali electrolysis. The system has a potential to produce hydrogen efficiently, at low cost, and in an environmentally benign way by maximizing the utilized solar spectrum and converting the byproducts into useful industrial commodities. Furthermore, by using electrodes as electron donors to drive photochemical hydrogen production, the hybrid system minimizes potential pollutant emissions. The products of the hybrid system are hydrogen, chlorine and sodium hydroxide, all of which are desired industrial commodities. The system production yield and efficiencies are investigated based on an operation temperature range of 20°C-80°C. A maximum energy efficiency of 42% is achieved between the temperatures of 40°C and 50°C.
Hydrogen represents a clean and high gravimetric energy density chemical fuel that could potentially replace fossil fuels and natural gas in electricity generation and powering vehicles. Central to the success of hydrogen technology and economy, the sustainability, efficiency and cost of hydrogen generation are the major factors. Industrial hydrogen is currently obtained from steam methane reforming and water-gas shift reaction, however, this method still relays on fossil fuels. Therefore, it is important to develop efficient, low-cost, and scalable method to produce hydrogen in a sustainable manner. Photoelectrochemical (PEC) water splitting to produce hydrogen is one of most promising and sustainable approaches. The development of low-cost and efficient nanostructured photoelectrodes is the key to achieve this goal. In this chapter, we will give a brief background on PEC water splitting and review the recent advancement of developing low-cost nanostructured photoelectrodes.
Lanthanum tantalum niobium oxynitride [La(Ta,Nb)O 2 N] powders were prepared with different Nb/Ta ratios by conventional solid state reaction. La(Ta,Nb)O 2 N photoanodes were fabricated by electrophoretic deposition of La(Ta,Nb)O 2 N suspension in acetone onto ITO substrate. The La(Ta,Nb)O 2 N photoanodes were found to exhibit photoelectrochemical activity for water oxidation reaction in alkaline solution. Subsequently, a cobalt-phosphate based oxygen evolution catalyst (CoPi-OEC) was photodeposited onto the surface of the La(Ta,Nb)O 2 N catalyst to improve the photoelectrochemical performance. In the presence of CoPi catalyst, the photocurrent-voltage characteristics of the La(Ta,Nb)O 2 N electrodes were enhanced with its effect more pronounced at lower potentials. A stable photocurrent density of 20 mA/cm 2 at 1.2 V vs SCE was achieved under the illumination using alkaline phosphate solution with pH 13. Relative to the La(Ta,Nb)O 2 N photoanodes, nearly three times higher photocurrent density was observed at 1.2 V vs SCE for a CoPi/La(Ta,Nb)O 2 N photoelectrode. Perovskite-based oxide-nitrides modified with suitable cocatalyst of CoPi, have been shown as a new pathway towards substantial photoelectrochemical current gain during the PEC water splitting reaction.
Lanthanum tantalum niobium oxynitride [La(Ta,Nb)O2N] powders were prepared with different Nb/Ta ratios by conventional solid state reaction. La(Ta,Nb)O2N photoanodes were fabricated by electrophoretic deposition of La(Ta,Nb)O2N suspension in acetone onto ITO substrate. The La(Ta,Nb)O2N photoanodes were found to exhibit photoelectrochemical activity for water oxidation reaction in alkaline solution. Subsequently, a cobalt-phosphate based oxygen evolution catalyst (CoPi-OEC) was photodeposited onto the surface of the La(Ta,Nb)O2N catalyst to improve the photoelectrochemical performance. In the presence of CoPi catalyst, the photocurrent-voltage characteristics of the La(Ta,Nb)O2N electrodes were enhanced with its effect more pronounced at lower potentials. A stable photocurrent density of 20 mA/cm2 at 1.2 V vs SCE was achieved under the illumination using alkaline phosphate solution with pH 13. Relative to the La(Ta,Nb)O2N photoanodes, nearly three times higher photocurrent density was observed at 1.2 V vs SCE for a CoPi/La(Ta,Nb)O2N photoelectrode. Perovskite-based oxide-nitrides modified with suitable cocatalyst of CoPi, have been shown as a new pathway towards substantial photoelectrochemical current gain during the PEC water splitting reaction.
In the present work we grow self-organized Ta2O5 nanotube layers in a H2SO4/NH4F electrolyte at various elevated temperatures. Under optimized conditions we obtain 4 μm long nanotubes that are well adherent to the substrate and can be grown very homogenous over large surface areas. Moreover, the key advantage of this approach is that an open top morphology (initiation layer free) is obtained. After a suitable conversion treatment in NH3 atmosphere Ta3N5 nanotubes are obtained, that after (Co-Pi+Co(OH)x) modification provide, under AM 1.5G illumination conditions, a photoelectrochemical current response of 4.7 mA cm−2 at +1.23 V vs RHE.
In this study, we have attempted to experimentally validate the results of previous theoretical calculations predicting the possible formation of the CdTiO₃₋ₓNy, CdNbO₂N, and CdTaO₂N phases by applying conventional one- and two-step fabrication methods under an NH₃ flow. For the two-step method, CdTiO₃, Cd₂Nb₂O₇, and Cd₂Ta₂O₇ crystals were first grown by a KCl flux method, and the effects of solute concentration and cooling rate on the crystal growth were studied. The formability of their (oxy)nitride derivatives was investigated by changing the nitridation temperature (750 to 950 °C) and time (1 to 10 h) of oxide precursors. It was found that the CdTiO₃₋ₓNy, CdNbO₂N, and CdTaO₂N phases cannot be formed by the applied methods due to the low volatilization temperature of cadmium and the susceptibility of titanium and niobium to reduction under an NH₃ atmosphere. Under high-temperature NH₃ atmosphere, only Cd₂Ta₂O₇ was fully converted to single-phase Ta₃N₅. The results from the photocatalytic O₂ evolution test over bare and CoOₓ-loaded Ta₃N₅ crystalline structures, converted from Cd₂Ta₂O₇ (Cd-Ta₃N₅) and Na₂CO₃-treated Ta₂O₅ (Na-Ta₃N₅) and Cd₂Ta₂O₇ (Na-Cd-Ta₃N₅) crystals by nitridation at 850 °C for 20 h under an NH₃ flow, revealed that the CoOₓ-loaded Na-Ta₃N₅ showed more than two times higher O₂ evolution rate (655 μmol), whereas the CoOₓ-loaded Cd-Ta₃N₅ and Na-Cd-Ta₃N₅ exhibited nearly four (501 μmol) and three (422 μmol) times higher O₂ evolution rates at 5 h compared with their bare counterparts. An improved photocatalytic activity for O₂ evolution is related to the higher density of nucleation centers of CoOₓ nanoparticles in the form of dangling bonds in porous Ta₃N₅ structures and long-lived photogenerated holes, as attested by time-resolved absorption spectroscopy.
Surface defects and impurities play important roles in the photocatalytic performance of semiconductors. In this study, DFT calculations are performed to investigate the effects of oxygen impurities and nitrogen vacancies on the surface stability and electronic structures of Ta3N5(100), (010) and (001) low-index surfaces. The results show that, for each surface, the oxygen impurities and nitrogen vacancies are beneficial and harmful, respectively, to the surface stability of Ta3N5. The oxygen impurities and nitrogen vacancies have mainly two effects on the surface electronic structures of Ta3N5. One is saturating surface states on the clean surface, and the other is inducing the downshift of conduction band minimum. In addition, the Ta3N5(100) surface with oxygen impurities is expected to have the strongest reduction ability in practice, providing useful guidance for further investigations of Ta3N5 in the photocatalytic hydrogen evolution.
Nano-TaOxNy oxygen reduction reaction (ORR) catalysts were supported on multi-walled carbon nanotubes (MWCNTs) using two step pyrolysis of oxy-tantalum phthalocyanine (TaOPc). For the first time, slightly oxidized Ta3N5 was experimentally proposed to be ORR active in acidic media.
In the present work we grow anodic self-organized Ta2 O5 nanotube layers, which are converted by ammonolysis to Ta3 N5 nanotubes, and then are used as photoanodes for photoanalytic water splitting. We introduce a two-step anodization process that not only improves order (reduced growth defects) and overall light absorption in the nanotube layers, but also provides a significantly reduced interface charge resistance at the nitride/metal interface due to subnitride (TaNx ) formation. As a result, such nanotube anodes afford a 15-fold increase of the photocurrent compared with conventional nanotubular Ta3 N5 electrodes under AM 1.5 G simulated sunlight (100 mW cm(-2) ) conditions.
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Ta oxynitride (TaOxNy) nanotubes (NTs) were synthesized by the anodization of Ta in an aqueous H2SO4 + HF solution, forming Ta oxide NTs, followed by the high temperature conversion of Ta oxide to TaOxNy in ammonia. The electrochemical behavior of these nanotubular arrays was then investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), revealing a wide range of interesting properties. The Ta oxynitride NTs, which are shown to contain evenly spaced holes along their length, undergo a reversible redox process involving cation intercalation in both aqueous solutions and dry acetonitrile at potentials negative of 0.5 V, while above this, the nanotubular array is non-conducting. From the CV charges, it is possible that this reaction occurs only on the exposed TaOxNy NT surfaces, although the nanotubular array does undergo conductivity and colour switching. EIS analysis has confirmed the pseudocapacitive properties of the TaOxNy NTs at < 0.5 V, while at potentials above this, Mott-Schottky analysis shows that they are n-type semiconductors having a donor density of ca. 6 × 1021 cm-3.
This paper describes an approach to synthesize tightly adhered Ta3N5 nanotube array (NTA) photoanode with enhanced electron conductivity between the Ta3N5 layer and the substrate via a two-step anodization method. The obtained tightly adhered Ta3N5 NTA photoanode exhibits excellent photoelectrochemical properties with an optimal photocurrent up to 5.3 mA cm-2 at 1.6 V vs. reversible hydrogen electrode. This approach provides an effective strategy to address the adhesion issue of one dimensional semiconductor photoanodes.
Novel Ag2O/N-doped helical carbon nanotubes (Ag2O/N-HCNTs) were successfully synthesized via a simple coprecipitation method and were well characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). The photocatalytic activities were evaluated in the degradation of methylene blue (MB) aqueous solution. The results showed that Ag2O nanoparticles sized 3-10 nm were highly anchored on the surface and inner tubes of the N-HCNTs support, and significantly enhanced the visible-light photocatalytic activity compared to bare Ag2O. It was attributed to the combined effects, including highly dispersed smaller Ag2O particles and higher charge separation efficiency. The possible mechanism for the photocatalytic activity of Ag2O/N-HCNTs was also tentatively proposed. In particular, the rate of degradation of the as-prepared Ag2O/N-HCNTs was 3.9 times faster than that of using bare Ag2O nanoparticles under visible light irradiation. Furthermore, the Ag2O/N-HCNTs could be easily recycled in visible photocatalytic activity. In addition, the Ag2O/N-HCNTs could also degrade MB dye in different water sources like Changjiang River water and tap water with high efficiency as well as in deionized water and that will greatly promote their application in the area of environmental remediation.
Incorporation of co-catalysts onto silicon-based nanomaterials has been diligently pursued as photocatalysts for water splitting. Here we employ a metal-assisted chemical etching method to fabricate different types (p type and n type) of silicon nanowire arrays (Si NWs), followed by the Pt deposition outside. The resulting Si NWs/Pt exhibits much enhanced photo-electrochemical properties, with higher photocurrent density and lower onset potential relative to the pristine silicon nanowire arrays and planar silicon due to the high surface roughness of silicon nanowire arrays and the addition of Pt catalyst. We have also demonstrated that different types of Si NWs/Pt show different enhancement effects for oxygen evolution reaction and hydrogen evolution reaction under illumination. This study demonstrates an excellent photo-electrochemical catalyst for water splitting and provides a valuable guidance for choosing the right type of silicon in terms of the target chemical reaction.
Hierarchically porous NaCoPO4-Co3O4 hollow microspheres are successfully synthesized via a simple hydrothermal method and calcination in air. It is found that the as-prepared hierarchically porous NaCoPO4-Co3O4 hollow microspheres exhibit good catalytic activity toward the oxidation of glucose, it shows a fast amperometric response time of less than 5 s, and the detection limit is estimated to be 0.125 µM. More importantly, compared with other normally co-existing electroactive species (such as ascorbic, uric acid and acid dopamine), the electrode modified with hierarchically porous NaCoPO4-Co3O4 hollow microspheres shows good selectivity. These results suggest that hierarchically porous NaCoPO4-Co3O4 hollow microspheres have promising application in electrocatalysts for quantitative determination of glucose with high sensitivity and selectivity.
Thin films of SnO2 are prepared by anodic oxidation of Sn on glass substrates. The surface topography of the anodic films is consistent with the original Sn films, indicating that the oxidation process primarily takes place perpendicularly along the Sn particles. As-prepared anodic SnO2
thin films possess an amorphous SnO2 phase at the surface, followed by an unoxidized thin layer of Sn between the SnO2
film and the substrate. With increasing annealing temperature, the residual Sn layer decreases until it disappears at 400 °C, and the amorphous SnO2 becomes nanocrystalline. The mobility of the as-prepared anodic SnO2
films is less than 0.1 cm2/(V s), but the annealed films have a mobility range of 1.6–2.2 cm2/(V s).
Ta2O5 films have been successfully fabricated on tantalum substrate via a facile hydrothermal route and characterized by a series of spectroscopic techniques. The morphology of the as-prepared Ta2O5 films showed great impacts on the photocatalytic activity. Without any co-catalysts, the as-prepared Ta2O5 films on tantalum exhibited remarkable photocatalytic activity and recyclability both in the degradation of rhodamine B and in the hydrogen production from water splitting under UV irradiation.
Photoelectrochemical (PEC) solar water splitting over oxynitrides is a promising process for renewable hydrogen production. However, the oxynitride heterojunction photoanodes with high charge-separation efficiency and stability, which have unique dimensionality-dependent integrative and synergic effects, are intriguing but still underdeveloped. Here, we design and fabricate the 1D/2D nanorod/nanosheet-assembled tantalum oxynitride (TaON) photoanode with the high PEC activity. Especially, integrated 3D heterojunction photoanodes comprising the 1D/2D barium-doped TaON (Ba-TaON) array and 2D carbon nitride (C3N4) nanosheets decorated with CoOx nanoparticles as a novel stack design were firstly prepared and the 3D CoOx/C3N4/Ba-TaON photoanodes with the remarkable photostability reached the pronounced photocurrent of 4.57 mA cm−2 at 1.23 V vs. RHE under AM 1.5G simulated sunlight. More broadly, the harness charge transfer process of this unique 3D heterojunction photoanode with the intrinsic requirements has been identified by the quantitative analysis combined with the electrochemical impedance and photoluminescence analysis. All the results highlight the great significance of the 3D dimensionality-dependent heterojunction as a promising photoelectrode model for the application in solar conversion. The cooperating amplification effects of nanoengineering from composition regulation, morphology innovation and heterojunction construction provide a valuable insight for creating more purpose-designed (oxy)nitride photoelectrodes with highly efficient performance.
Tantalum nitride (Ta3N5) and oxynitride (TaON) are promising materials for photoelectrochemical (PEC) water splitting due to near-ideal band gaps and band edge positions. However, the high-temperature ammonolysis process that is usually used to make these materials depends sensitively on the process parameters and specific design of the annealing system, and reproducing highly efficient (oxy)nitride photoanodes from recipes reported by other laboratories has proven to be challenging. To understand and monitor the nitridation process in more detail, we employ an optical absorption spectroscopy technique that allows us to follow the transformation of thin Ta2O5 films in situ at temperatures up to 800 degrees C. Our results show that the incorporation of nitrogen in a dry ammonia atmosphere starts at 575 degrees C and is accompanied by a gradual red-shift of the Ta2O5 absorption edge and an expansion of the lattice due to the larger ionic radius of N-3 relative to O-2. Although coloration of the material due to an N-2p ? Ta-3d transition occurs readily, the films do not show any visible-light PEC activity until the nitrogen concentration is high enough to form a continuous N-2p impurity band. Ta3N5 is found to be the only thermodynamically stable phase between 575 and 800 degrees C, with no traces of TaON. Longer nitridation times result in lower defect concentrations, larger grain sizes, and improved PEC performance. The photocurrent of well-crystallized films is limited by slow water oxidation kinetics. This can be effectively remedied by depositing IrO2 nanoparticles as a water oxidation cocatalyst, which results in external quantum efficiencies of up to 45%. The smaller enhancement of the PEC performance at longer wavelengths reveals that hole transport in Ta3N5 limits the water splitting performance of IrO2-catalyzed Ta3N5 photoanodes.
Herein, we report the preparation, characterization and investigation of previously unexplored W incorporated iron vanadate (FeVO4) electrodes for solar light driven water oxidation in photoelectrochemical cell. The W incorporated FeVO4 films on F-doped SnO2 substrates have been prepared by layer-by-layer deposition of metal organic precursor and subsequent thermal decomposition at 550 degrees C in air. The synthesized films with a band gap of about 2.06 eV are responsive to visible light up to wavelength of similar to 600 nm, i.e. being able to harvest similar to 45% of the solar spectrum. The W incorporated FeVO4 photoanodes are active materials for photoelectrochemical water oxidation and, yield a significantly enhanced (2.5 fold higher) photocurrent in comparison to pristine FeVO4 photoanodes. This improvement can be attributed to increased n-type conductivity by W6+ ion doping in the FeVO4 lattice. The incident photon to current conversion efficiency achieved with developed photoanodes is as high as 6.5% at 400 nm. Copyright
Semiconductor-based photocatalysis and photoelectrocatalysis have received considerable attention as alternative approaches for solar energy harvesting and storage. The photocatalytic or photoelectrocatalytic performance of a semiconductor is closely related to the design of the semiconductor at the nanoscale. Among various nanostructures, one-dimensional (1D) nanostructured photocatalysts and photoelectrodes have attracted increasing interest owing to their unique optical, structural, and electronic advantages. In this article, a comprehensive review of the current research efforts towards the development of 1D semiconductor nanomaterials for heterogeneous photocatalysis and photoelectrocatalysis is provided and, in particular, a discussion of how to overcome the challenges for achieving full potential of 1D nanostructures is presented. It is anticipated that this review will afford enriched information on the rational exploration of the structural and electronic properties of 1D semiconductor nanostructures for achieving more efficient 1D nanostructure-based photocatalysts and photoelectrodes for high-efficiency solar energy conversion.
Cooperative photoelectrochemical (PEC) conversion of solar energy into chemical fuels is considered as one of the most promising solutions to the sustainable energy needs of mankind, considering the intermittent and spatial fluctuations in the availability of sunlight on earth. The development of synthetic visible-light-driven semiconductor catalysts that functionally mimic the elegant water reduction chemistry of hydrogenase enzymes has attracted widespread interest and also created a lot of systems. Organic water oxidation catalysts based on earth-abundant elements are more promising due to low manufacturing cost, abundance, and environmental sustainability. Toward such applications, a strategy for fabricating CN films should be developed. Generally, a successful photoelectrochemical device requires not only a high surface area, but also an optimization of the morphology and quality of the film, including the contact with the conductive substrate, the film thickness, and the size of the light harvesting microstructures.
The physicochemical properties of a tantalum nitride (Ta3N5) photoanode were investigated in detail to understand fundamental aspects associated with the photoelectrochemical (PEC) water oxidation. The Ta3N5 thin films were synthesized using DC magnetron sputtering followed by annealing in air and nitridation under ammonia (NH3). The polycrystalline structure with a dense morphology of the monoclinic Ta3N5 films was obtained. A relatively low absorption coefficient (104 to 105 cm−1) in the visible light range was measured for Ta3N5, consistent with the nature of indirect band-gap. Ultra-fast spectroscopic measurements revealed that the Ta3N5 films possess low transport properties and have especially fast carrier recombination (< 10 ps) for the samples with various thickness. These critical kinetic properties of Ta3N5 as a photoanode may necessitate high overpotentials to achieve appreciable photocurrents for water oxidation (onset ~0.6 V vs. RHE).
This work shows that highly ordered and mechanically stable micrometer-long Ta2O5 nanotube arrays can be fabricated by galvanostatic anodization in a few seconds. Typically, ~ 7.7 μm long nanotubes can be grown at 1.2 A cm− 2 in only 2 s. Such nanotubes can be converted to Ta3N5 nanotube arrays by nitridation. Photoelectrochemical (PEC) water splitting using AM 1.5G illumination yields for the Ta3N5 nanotube photoanode modified with cobalt phosphate (Co-Pi) remarkable photocurrents of 5.9 mA cm −2 at 1.23 VRHE and 12.9 mA cm −2 at 1.59 VRHE and after Ba-doping a value of 7.5 mA cm −2 at 1.23 VRHE is obtained.
Ta3N5 is a promising photoanode candidate for photoelectrochemical water splitting, with a band gap of about 2.1 eV and a theoretical solar-to-hydrogen efficiency as high as 15.9 % under AM 1.5 G 100 mW cm−2 irradiation. However, the presently achieved highest photocurrent (ca. 7.5 mA cm−2) on Ta3N5 photoelectrodes under AM 1.5 G 100 mW cm−2 is far from the theoretical maximum (ca. 12.9 mA cm−2), which is possibly due to serious bulk recombination (poor bulk charge transport and charge separation) in Ta3N5 photoelectrodes. In this study, we show that volatilization of intentionally added Ge (5 %) during the synthesis of Ta3N5 promotes the electron transport and thereby improves the charge-separation efficiency in bulk Ta3N5 photoanode, which affords a 320 % increase of the highest photocurrent comparing with that of pure Ta3N5 photoanode under AM 1.5 G 100 mW cm−2 simulated sunlight.
In this study, we conceptually develop and thermodynamically analyze a new continuous-type hybrid system for hydrogen production which photoelectrochemically splits water and performs chloralkali electrolysis. The system has a potential to produce hydrogen efficiently, at low cost, and in an environmentally benign way by maximizing the utilized solar spectrum and converting the byproducts into useful industrial commodities. Furthermore, by using electrodes as electron donors to drive photochemical hydrogen production, the hybrid system minimizes potential pollutant emissions. The products of the hybrid system are hydrogen, chlorine and sodium hydroxide, all of which are desired industrial commodities. The system production yield and efficiencies are investigated based on an operation temperature range of 20 °C–80 °C. A maximum energy efficiency of 42% is achieved between the temperatures of 40 °C and 50 °C.
Despite the fact that Ta3N5 absorbs a major fraction of the visible spectrum, the rapid decrease of photocurrent encountered in water photoelectrolysis over time remains a serious hurdle for the practical application of Ta3N5 photoelectrodes. Here, by employing a Co3O4 nanoparticle water oxidation catalyst (WOC) as well as an alkaline electrolyte, the photostability of Ta3N5 electrode is significantly improved. Co3O4/Ta3N5 photoanode exhibits the best durability against photocorrosion to date, when compared with Co(OH)x/Ta3N5 and IrO2/Ta3N5 photoanodes. Specifically, about 75% of the initial stable photocurrent remains after 2 h irradiation at 1.2 V vs. RHE (reversible hydrogen electrode). Meanwhile, a photocurrent density of 3.1 mA cm−2 has been achieved on Co3O4/Ta3N5 photoanode at 1.2 V vs. RHE with backside illumination under 1 sun AM 1.5 G simulated sunlight. The reason for the relatively high stability is discussed on the basis of electron microscopic observations and photoelectrochemical measurements, and the surface nitrogen content is monitored by X-ray photoelectron spectroscopic analysis.
Amorphous Ta-O nanotubes (NTs) prepared by anodization in a sulfuric-acid-based solution have been found to contain considerable amounts of extra oxygen and sulfur. Their structural and thermal stability has been studied by combining x-ray diffractometry, transmission electron microscopy, and thermal analysis. The amorphous Ta-O, whose composition was estimated to be Ta2O6.6S0.7, crystallizes into orthorhombic -Ta2O5 at temperatures around 1073 K by an endothermic reaction, at which excess oxygen and impurity sulfur are released. The amorphous NTs were found to be thermally more stable than stoichiometric amorphous Ta2O5, whose crystallization temperature is around 973 K. Excess oxygen and impurity sulfur, which form chemical bonds with Ta atoms in the amorphous solid, must be the origin of the stability. The crystallization follows the out-diffusion of oxygen and sulfur from the solid at temperatures where the mobility of atoms is high enough, indicating that the crystallization is kinetically arrested.
Harvesting energy directly from sunlight is a very attractive and desirable way to solve the rising energy demand. In the past few decades, considerable efforts have been focused on identifying appropriate materials and devices that can utilize solar energy to produce chemical fuels. Among these, one of the most promising options is the construction of a photoelectrochemical (PEC) cell that can produce hydrogen fuel or oxygen from water. Significant advancement in the understanding and construction of efficient photoanodes to improve performance has been accomplished within a short period of time owing to various newly developed ideas and approaches, including facilitating charge transportation in narrow band gap semiconductors or doping in wide band gap semiconductors for enhancing visible-light absorption; electrocatalysts for decreasing overpotentials; controlling the morphology of the materials for enhancing light absorption and shortening the transfer distance of minority carriers; and other methods such as using heterojunction structures for band-structure engineering, sensitization, and passivating layers. In this review, we focus on the recent developments of some promising visible-light active photoanode materials with high PEC performance, such as BiVO4, α-Fe2O3, WO3, TaON, and Ta3N5.
Multilayer Ta3 N5 hollow sphere-nanofilms with precisely tunable numbers of layers are successfully fabricated by the combination of oil-water interfacial self-assembly strategy and the controllable sol-gel reaction of precursors. The photoelectrochemical water splitting properties of the as-obtained Ta3 N5 hollow sphere-nanofilms are significantly enhanced and found to be highly dependent on the layer numbers of the nanofilms.
Tantalum zirconium oxynitride phases Ta(3-x)Zr(x)N(5-x)O(x) (0 ≤ x ≤ 0.66) having the Ta3N5 structure and Ta(1-x)Zr(x)N(1−x)O(1+x) (0 ≤ x ≤ 0.28) with the TaON structure have been prepared by solid state-gas syntheses. Oxide precursors have been prepared by a novel sol-gel process variant, using a mixture of acetic acid and acetic anhydride as solvent. The optical properties of the brilliantly coloured pigment quality Ta(3-x)Zr(x)N(5-x)O(x) (0 ≤ x ≤ 0.66) semiconducting oxynitrides have been examined by UV-VIS remission spectroscopy. Their applicability for an industrial scale production and a widespread use as brilliant, lightfast and inert inorganic colouring agents has been investigated. These pigments may be useful for colouring paints, plastics and medium temperature ceramic applications, replacing comtemporary toxic metal containing pigments.