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Electrochemical co-upgrading CO 2 and glycerol for selective formate production with 190% overall Faradaic efficiency
Nano Research
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The electrocatalytic nitrate reduction (NO3RR) holds significance in both NH3 synthesis and nitrate contamination remediation. However, achieving industrial‐scale current and high stability in membrane electrode assembly (MEA) electrolyzer remains challenging due to inherent high full‐cell voltage for sluggish NO3RR and water oxidation. Here, Cu2NCN with positive surface electrostatic potential VS(r) is applied as highly efficient NO3RR electrocatalysts to achieve industrial‐current and low‐voltage stable NH3 production in MEA electrolyzer with coupled anodic glycerol oxidation. This paired electro‐refinery (PER) system reaches 4000 mA cm⁻² at 2.52 V and remains stable at industrial‐level 1000 mA cm⁻² for 100 h with the NH3 production rate of 97000 µgNH3 h⁻¹ cm⁻² and a Faradaic efficiency of 83%. Theoretical calculations elucidate that the asymmetric and electron‐withdrawing [N−C≡N] units enhance polarization and VS(r), promoting robust and asymmetric adsorption of NO3* on Cu2NCN to facilitate O−N bond dissociation. A comprehensive techno‐economic analysis demonstrates the profitability and commercial viability of this coupled system. Our work opens a new avenue and marks a significant advancement in MEA systems for industrial NH3 synthesis.
Glycerol electrooxidation (GOR), as an innovative strategy for the production of value‐added chemicals, is considered a promising anodic alternative to oxygen evolution reaction in electrocatalysis. However, the high potential and the limited selectivity and faradaic efficiency impede the industrial‐scale application toward GOR. Herein, we for the first time constructed rhenium and ruthenium co‐doped transition metal alloy (NiCoFeRuRe) for the efficient electrooxidation of glycerol to formate. Benefiting from the rapid generation of M³⁺‐OOH induced by Ru element and the inhibition of OER and excessive oxidation of glycerol by Re species through in situ chacterization, the optimized NiCoFeRuRe requires only 1.133 VRHE to achieve a current density of 10 mA cm⁻², a faradaic efficiency of 95.6 % for formate product with a stability more than 450 h. Importantly, employing NiCoFeRuRe as a bifunctional catalyst, the cell is constructed to produce hydrogen and formate simultaneously, which is 265 mV lower than the electrolytic water splitting owning an excellent stability of 350 h. This work provides a facile strategy for rationally designing high‐performance GOR catalysts for biomass upgradings.
The electrocatalytic glycerol oxidation reaction (GOR) represents a mild and sustainable pathway to produce value‐added chemicals such as formate. However, the rational design and controlled synthesis of efficient catalysts to achieve highly selective C−C bond cleavage of glycerol towards formate remains a great challenge. Herein, atomic Pd doped Cu3N hollow nanocubes with Pd−Cu dual sites were prepared via the unique Kirkendall process, exhibiting superior electrocatalytic GOR activity and selectivity towards formate with a maximum Faraday efficiency of 91.6 %. In situ spectroscopic characterization and theoretical calculations reveal that Pd atoms located in partial Cu substituent sites could facilitate the generation of active *OH and enhance the adsorption of glycerol molecule on adjacent Cu sites, while Pd atoms located in Cu3N unit center could effectively reduce the energy barrier of C−C bond cleavage for the rate determining step. Our work provides new insights into the development of well‐defined dual‐site catalysts to boost glycerol electrooxidation to formate.
Photoelectrochemistry (PEC) presents a direct pathway to solar fuel synthesis by integrating light absorption and catalysis into compact electrodes. Yet, PEC hydrocarbon production remains elusive due to high catalytic overpotentials and insufficient semiconductor photovoltage. Here we demonstrate ethane and ethylene synthesis by interfacing lead halide perovskite photoabsorbers with suitable copper nanoflower electrocatalysts. The resulting perovskite photocathodes attain a 9.8% Faradaic yield towards C2 hydrocarbon production at 0 V against the reversible hydrogen electrode. The catalyst and perovskite geometric surface areas strongly influence C2 photocathode selectivity, which indicates a role of local current density in product distribution. The thermodynamic limitations of water oxidation are overcome by coupling the photocathodes to Si nanowire photoanodes for glycerol oxidation. These unassisted perovskite–silicon PEC devices attain partial C2 hydrocarbon photocurrent densities of 155 µA cm⁻², 200-fold higher than conventional perovskite–BiVO4 artificial leaves for water and CO2 splitting. These insights establish perovskite semiconductors as a versatile platform towards PEC multicarbon synthesis.
Electrocatalytic glycerol oxidation reaction (GOR) to produce high‐value formic acid (FA) is hindered by high formation potential of active species and sluggish C−C bond cleavage kinetics. Herein, Ni single‐atom (NiSA) and Co single‐atom (CoSA) dual sites anchored on nitrogen‐doped carbon nanotubes embedded with Ni0.1Co0.9 alloy (Ni0.1Co0.9@NiSACoSA‐NCNTs) are constructed for electrochemical GOR. Remarkably, it can reach 10 mA cm⁻² at a low potential of 1.15 V versus the reversible hydrogen electrode (vs. RHE) and realize a high formate selectivity of 93.27 % even at high glycerol conversion of 98.81 % at 1.45 V vs. RHE. The GOR mechanism and pathway are systematically elucidated via experimental analyses and theoretical calculations. It is revealed that the active hydroxyl (*OH) can be produced during the GOR. The NiSA, CoSA, and Ni0.1Co0.9 synergistically optimizes the electronic structure of CoSA active sites, reducing the energy barriers of *OH‐mediated cleavage of C−C bonds and dehydrogenation of C1 intermediates. This decreases the number of reaction intermediates and reaction steps of GOR‐to‐FA, thus increasing the formate production efficiency. After coupling GOR with hydrogen evolution reaction in a membrane electrode assembly cell, 14.26 g of formate and 23.10 L of H2 are produced at 100 mA cm⁻² for 108 h.
The electrocatalytic conversion of carbon dioxide (CO2) to formate is significant for carbon neutrality. How to improve the reaction kinetics of electrocatalysts is one of the important challenges. An innovative electrodeposition strategy is presented herein to rationally synthesize the vanadium oxide (VOx) clusters decorated Bi‐Sn alloy (BiSn(VOx)) catalyst. Theoretical and in situ spectral studies confirm the simultaneously improved kinetics of CO2 activation and subsequent protonation via VOx clusters mediated water dissociation process, thereby optimizing the electrocatalytic activity and selectivity of CO2 to formate. Remarkably, this BiSn(VOx) catalyst achieves high Faradic efficiency (FE) of formate over 90% within wide potential window of 800 mV and excellent stability over 100 h at −0.6 V versus RHE. Moreover, the BiSn(VOx) cathode integrated rechargeable Zn‐CO2 battery realizes the largest power density of 3.8 mW cm⁻², while the assembled co‐electrolysis electrolyzer delivers a total FE of formate over 182% at a cell voltage of 0.6 V, outperforming the highest value so far. The work provides a promising way to develop advanced electrocatalysts for electrolysis.
Electrochemical glycerol oxidation reaction (GOR) is a promising candidate to couple with cathodic reaction, like hydrogen evolution reaction, to produce high‐value product with less energy consumption. Two dimensional conjugated metal–organic frameworks (2D c‐MOFs), comprising square‐planar metal‐coordination motifs (e.g., MO4, M(NH)4, MS4), are notable for their programable active sites, intrinsic charge transport, and excellent stability, making them promising catalyst candidates for GOR. In this study, we introduce a novel class of 2D c‐MOFs electrocatalysts, M2[NiPcS8] (M=Co/Ni/Cu), which are synthesized via coordination of octathiolphthalocyaninato nickel (NiPc(SH)8) with various metal centers. Due to a fast kinetic and high activity of CoS4 sites for GOR, the electrocatalytic tests demonstrate that Co2[NiPcS8] supported on carbon paper displays a low GOR potential of 1.35 V vs. RHE at 10 mA cm⁻², significantly reducing the overall water‐electrolysis‐voltage reduction by 0.27 V from oxygen evolution reaction to GOR, thereby outperforming Ni2[NiPcS8] and Cu2[NiPcS8]. Additionally, we have determined that the GOR activity of CoX4 linkage sites varies with different heteroatoms, following an experimentally and theoretically confirmed activity order of CoS4>CoO4>Co(NH)4. The GOR performance of Co2[NiPcS8] not only demonstrate superior performance among non‐noble metal complex, but also provides critical insights on designing high‐performance MOF electrocatalysts upon optimizing the electronic environment of active sites.
The significant increase in demand for fuels and chemicals driven by global economic expansion has exacerbated concerns over fossil fuel consumption and environmental pollution. To achieve sustainable production of fuels and chemicals, biomass resources provide a rich repository for carbon‐neutral, green renewable energy, and organic carbon. This paper reviews the transformation and utilization of lignocellulosic biomass and its derivatives, emphasizing their valorization into high‐quality chemicals and biofuels. The advantages and disadvantages of various pretreatment methods are discussed based on the composition of lignocellulose. Furthermore, the methods and pathways for the valorization and conversion of cellulose, hemicellulose, and lignin are detailed according to the unique functional groups of different lignocellulosic platform molecules. However, the complex and resilient structure of biomass presents challenges for the disassembly and utilization of single components, and achieving high yields and selectivity for target products remains difficult. In conclusion, this paper comprehensively reviews the various types and pretreatment technologies of lignocellulose, focusing on the methods and pathways for the valorization of lignocellulosic biomass and its derivatives, thereby providing clear guidance and insights for optimizing lignocellulose utilization in the future.
Renewable energy is essential for power system decarbonization, but extended and unexpected periods of extremely low wind and solar resources (i.e., wind and solar droughts) pose a threat to reliability. The challenge is further exacerbated if shortages of the two occur simultaneously or if they affect neighboring grids simultaneously. Here we present a framework to characterize these events and propose three metrics to comprehensively assess renewable energy quality: resource availability, variability, and extremeness. An examination of long-term data across a vast geographical region shows a strong spatial correlation and temporal coincidence of renewable energy droughts. It also finds a lack of sites that excel in all three quality attributes, which presents a trilemma to investors, system planners, and policymakers. These findings underscore the significance of considering factors beyond mere resource availability and contribute to developing informed strategies for the reliable and sustainable deployment of variable energy resources.
Ethylene glycol electro‐oxidation reaction (EGOR) on nickel‐based hydroxides (Ni(OH)2) represents a promising strategy for generating value‐added chemicals, i.e. formate and glycolate, and coupling water‐electrolytic hydrogen production. The high product selectivity was one of the most significant area of polyols electro‐oxidation process. Yet, developing Ni(OH)2‐based EGOR electrocatalyst with highly selective product remains a challenge due to the unclear cognition about the EGOR mechanism. Herein, Mn‐doped Ni(OH)2 catalysts were utilized to investigate the EGOR mechanism. Experimental and calculation results reveal that the electronic states of eg* band play an important role in the catalytic performance and the product selectivity for EGOR. Broadening the eg* band could effectively enhance the adsorption capacity of glyoxal intermediates. On the other hand, this enhanced adsorption could lead to reduced side reactions associated with glycolate formation, simultaneously promoting the cleavage of C−C bonds. Consequently, the selectivity for formate was notably augmented by these enhancements. This work offers new insights into the regulation of catalyst electronic states for improving polyol electrocatalytic activity and product selectivity.
Recently, Ni‐based chalcogenides havedemonstrated remarkable activity and selectivity for alcohol electrooxidation, but the mechanisms remain debated. This study synthesizes Ni‐based electrodeswith different chalcogen anion coordination on nickel nanorod arrays (NiOx/Ni,NiSx/Ni, and NiSex/Ni NRAs). NiSex/Ni NRAsshowcases superior performance (Faradaic efficiency 92.9%) in glycerolelectrooxidation reaction (GOR). In situ spectroscopy reveals that NiSecoordination inhibits deep oxidative reconstruction of the Ni‐based interface, preventingNiOOH phase formation during GOR, enhancing activity and stability of NiSex/NiNRAs. Conversely, NiS and NiO coordination lead to deep reconstruction with NiOOHphase formation, limiting GOR performance. Differently, during competingreaction of GOR, the oxygen evolution reaction (OER) leads to deepreconstruction of NiSex interface due to the instability of Ni‐Sebonds, inducing performance degradation and dissolution of Se components. Furthermechanism investigation elucidates that the rate‐determining step (RDS) ofGOR at the NiSex interface involves oxidation of *C2H3O3 intermediatesthrough H2O adsorption, favoring stable formate production.Contrarily, the RDS at the NiSx, NiOx, and NiOOHinterfaces predominantly focus on the decarboxylation of multi‐carbon intermediates, raisingenergy barriers and over‐oxidizing formate to CO2. These results providenew insights for designing Ni‐based non‐oxide catalysts forefficient and stable electrocatalytic oxidation.
The practical application of the electrocatalytic CO2 reduction reaction (CO2RR) to form formic acid fuel is hindered by the limited activation of CO2 molecules and the lack of universal feasibility across different pH levels. Herein, we report a doping‐engineered bismuth sulfide pre‐catalyst (BiS‐1) that S is partially retained after electrochemical reconstruction into metallic Bi for CO2RR to formate/formic acid with ultrahigh performance across a wide pH range. The best BiS‐1 maintains a Faraday efficiency (FE) of ~95 % at 2000 mA cm⁻² in a flow cell under neutral and alkaline solutions. Furthermore, the BiS‐1 catalyst shows unprecedentedly high FE (~95 %) with current densities from 100 to 1300 mA cm⁻² under acidic solutions. Notably, the current density can reach 700 mA cm⁻² while maintaining a FE of above 90 % in a membrane electrode assembly electrolyzer and operate stably for 150 h at 200 mA cm⁻². In situ spectra and density functional theory calculations reveals that the S doping modulates the electronic structure of Bi and effectively promotes the formation of the HCOO* intermediate for formate/formic acid generation. This work develops the efficient and stable electrocatalysts for sustainable formate/formic acid production.
Electrochemical glycerol oxidation features an attractive approach of converting bulk chemicals into high‐value products such as glyceric acid. Nonetheless, to date, the major product selectivity has mostly been limited as low‐value C1 products such as formate, CO, and CO2, due to the fast cleavage of carbon‐carbon (C−C) bonds during electro‐oxidation. Herein, the study develops an atomically ordered Ni3Sn intermetallic compound catalyst, in which Sn atoms with low carbon‐binding and high oxygen‐binding capability allow to tune the adsorption of glycerol oxidation intermediates from multi‐valent carbon binding to mono‐valent carbon binding, as well as enhance *OH binding and subsequent nucleophilic attack. The Ni3Sn electrocatalyst exhibits one of the highest glycerol‐to‐glyceric acid performances, including a high glycerol conversion rate (1199 µmol h–1) and glyceric acid selectivity (62 ± 3%), a long electrochemical stability of > 150 h, and the capability of direct conversion of crude glycerol (85% purity) into glyceric acid. The work features the rational design of highly ordered catalytic sites for tailoring intermediate binding and reaction pathways, thereby facilitating the efficient production of high‐value chemical products.
Organic oxidation reactions (OORs) powered by renewable energy sources are gaining importance as a favorable alternative to oxygen evolution reaction, with the promise of reducing the cell potential and enhancing the overall viability of the water electrolysis. This comprehensive review delves into the electrochemical oxidation of diverse organic compounds, including alcohols, aldehydes, amines, and urea, as well as biomass‐derived renewable feedstocks such as hydroxymethylfurfural and glycerol. The key focus centers on the role of nickel (Ni)‐based catalysts for these OORs. The unique redox activity and chemical nature of Ni have been proven instrumental for the sustainable and cost‐effective oxidation of various organic molecules more efficiently and selectively. This review article discusses how strategic choices, such as the selection of foreign metals, intercalating species, vacancies, defects, and a secondary element (e.g. chalcogens and non‐metals), contribute to tuning the electrochemical performances of a Ni‐based (pre)catalyst for OORs. Moreover, this review provides insights into the active species in various reaction environments and further explores reaction mechanisms, to apparent phase changes of the catalyst with the most relevant examples. Finally, the review not only elucidates the limitations of the current approaches but also outlines potential avenues for future advancements in OOR.
Electrocatalytic CO2 reduction (CO2RR) to alcohols offers a promising strategy for converting waste CO2 into valuable fuels/chemicals but usually requires large overpotentials. Herein, we report a catalyst comprising unique oxygen-bridged Cu binuclear sites (CuOCu-N4) with a Cu···Cu distance of 3.0−3.1 Å and concomitant conventional Cu−N4 mononuclear sites on hierarchical nitrogen-doped carbon nanocages (hNCNCs). The catalyst exhibits a state-of-the-art low overpotential of 0.19 V (versus reversible hydrogen electrode) for ethanol and an outstanding ethanol Faradaic efficiency of 56.3% at an ultralow potential of −0.30 V, with high-stable Cu active-site structures during the CO2RR as confirmed by operando X-ray adsorption fine structure characterization. Theoretical simulations reveal that CuOCu-N4 binuclear sites greatly enhance the C−C coupling at low potentials, while Cu-N4 mononuclear sites and the hNCNC supportincrease the local CO concentration and ethanol production on CuOCu-N4. This study provides a convenient approach to advanced Cu binuclear site catalysts for CO2RR to ethanol with a deep understanding of the mechanism.
Preventing the deactivation of noble metal-based catalysts due to self-oxidation and poisonous adsorption is a significant challenge in organic electro-oxidation. In this study, we employ a pulsed potential electrolysis strategy for the selective electrocatalytic oxidation of glycerol to glyceric acid over a Pt-based catalyst. In situ Fourier-transform infrared spectroscopy, quasi-in situ X-ray photoelectron spectroscopy, and finite element simulations reveal that the pulsed potential could tailor the catalyst’s oxidation and surface micro-environment. This prevents the overaccumulation of poisoning intermediate species and frees up active sites for the re-adsorption of OH adsorbate and glycerol. The pulsed potential electrolysis strategy results in a higher glyceric acid selectivity (81.8%) than constant-potential electrocatalysis with 0.7 V RHE (37.8%). This work offers an efficient strategy to mitigate the deactivation of noble metal-based electrocatalysts.
In recent years, electrocatalytic systems powered by renewable energy have gained prominence in regard to sustainable chemical production. A majority of published literature focuses on catalyst development in alkaline electrolytes, driven by advantages such as high ionic conductivity, low charge transfer resistance and rapid kinetics. Here we shed light on challenges arising from the use of alkaline electrolytes for product separation and electrolyte recovery. Delving into acid–base reaction chemistry, we identify the problematic synthesis of organic acids whereby the high-pH environment leads to dissociation or deprotonation, forming conjugate bases and water. Our analysis of an alkaline electrochemical process for glycerol oxidation highlights the significant economic hurdles, with >60% of capital costs, 70% of raw material (for example, potassium hydroside) costs and 64% of total energy costs attributed to downstream product separation. These challenges, related to acid–base reaction chemistry, are often overlooked at the catalyst development stage, resulting in a significant waste of research resources.
The production of formic acid via electrochemical CO2 reduction may serve as a key link for the carbon cycle in the formic acid economy, yet its practical feasibility is largely limited by the quantity and concentration of the product. Here we demonstrate continuous electrochemical CO2 reduction for formic acid production at 2 M at an industrial‐level current densities (i.e., 200 mA cm⁻²) for 300 h on membrane electrode assembly using scalable lattice‐distorted bismuth catalysts. The optimized catalysts also enable a Faradaic efficiency for formate of 94.2 % and a highest partial formate current density of 1.16 A cm⁻², reaching a production rate of 21.7 mmol cm⁻² h⁻¹. To assess the practicality of this system, we perform a comprehensive techno‐economic analysis and life cycle assessment, showing that our approach can potentially substitute conventional methyl formate hydrolysis for industrial formic acid production. Furthermore, the resultant formic acid serves as direct fuel for air‐breathing formic acid fuel cells, boasting a power density of 55 mW cm⁻² and an exceptional thermal efficiency of 20.1 %.
Electrolysis that reduces carbon dioxide (CO2) to useful chemicals can, in principle, contribute to a more sustainable and carbon-neutral future1–6. However, it remains challenging to develop this into a robust process because efficient conversion typically requires alkaline conditions in which CO2 precipitates as carbonate, and this limits carbon utilization and the stability of the system7–12. Strategies such as physical washing, pulsed operation and the use of dipolar membranes can partially alleviate these problems but do not fully resolve them11,13–15. CO2 electrolysis in acid electrolyte, where carbonate does not form, has therefore been explored as an ultimately more workable solution16–18. Herein we develop a proton-exchange membrane system that reduces CO2 to formic acid at a catalyst that is derived from waste lead–acid batteries and in which a lattice carbon activation mechanism contributes. When coupling CO2 reduction with hydrogen oxidation, formic acid is produced with over 93% Faradaic efficiency. The system is compatible with start-up/shut-down processes, achieves nearly 91% single-pass conversion efficiency for CO2 at a current density of 600 mA cm⁻² and cell voltage of 2.2 V and is shown to operate continuously for more than 5,200 h. We expect that this exceptional performance, enabled by the use of a robust and efficient catalyst, stable three-phase interface and durable membrane, will help advance the development of carbon-neutral technologies.
Electrocatalytic CO2 reduction at near-ambient temperatures requires a complex inventory of protons, hydroxyls, carbonate ions and alkali-metal ions at the cathode and anode to be managed, necessitating the use of ion-selective membranes to regulate pH. Anion-exchange membranes provide an alkaline environment, allowing CO2 reduction at low cell voltages and suppression of hydrogen evolution while maintaining high conversion efficiencies. However, the local alkaline conditions and the presence of alkali cations lead to problematic carbonate formation and even precipitation. Here we report a pure-water-fed (alkali-cation-free) membrane–electrode–assembly system for CO2 reduction to ethylene by integrating an anion-exchange membrane and a proton-exchange membrane at the cathode and anode side, respectively, under forward bias. This system effectively suppresses carbonate formation and prevents salt precipitation. A scaled-up electrolyser stack achieved over 1,000 h stability without CO2 and electrolyte losses and with 50% Faradaic efficiency towards ethylene at a total current of 10 A.
Thermodynamically favorable electrooxidation of organics coupled with hydrogen production as an alternative to overall water splitting is rapidly developing due to low energy consumption and high value. But understanding the relationship between catalyst reconstruction and performance in depth remains a challenge. Herein, DFT calculations are used as a theoretical guide to adjust the local coordination environment and electronic structure of Ni3S2 by Fe doping, which promotes the self‐reconstruction of catalyst and nitrile evolution reaction performance. The overall reaction of benzylamine electrooxidation coupled with hydrogen production achieves a 14.5‐fold improvement in hydrogen production compared to water electrolysis at the same potential, almost completely converting benzylamine to high‐value benzonitrile (99% product yield). In situ spectroscopy and X‐ray absorption fine structure spectroscopy demonstrate that the excellent electrocatalytic performance due to Fe doping induces surface self‐reconstruction of Ni3S2 to NiOOH at low potential, and significantly reduces the rate‐determining step energy barriers for CN bonds to CN bonds. This work provides theoretical guidance in designing and preparing efficient catalysts for the electrosynthesis of nitrile compounds coupled with hydrogen production.
Electrocatalytic CO2 reduction processes are generally coupled with the oxidation of water. Process economics can greatly improve by replacing the water oxidation with a more valuable oxidation reaction, a process called paired electrolysis. Here we report the feasibility of pairing CO2 reduction with the oxidation of glycerol on Ni3S2/NF anodes to produce formate at both anode and cathode. Initially we optimized the oxidation of glycerol to maximize the Faraday efficiency to formate by using design of experiments. In flow cell electrolysis, excellent selectivity (up to 90 % Faraday efficiency) was achieved at high current density (150 mA/cm² of geometric surface area). Then we successfully paired the reduction of CO2 with the oxidation of glycerol. A prerequisite for industrial application is to obtain reaction mixtures with a high concentration of formate to enable efficient downstream separation. We show that the anodic process is limited in formate concentration, as Faraday efficiency to formate greatly decreases when operating at 2.5 M formate (∼10 w%) in the reaction mixture due to over‐oxidation of formate. We identify this as a major bottleneck for the industrial feasibility of this paired electrolysis process.
Nanostructured metal-nitrides have attracted tremendous interest as a new generation of catalysts for electroreduction of CO2, but these structures have limited activity and stability in the reduction condition. Herein, we report a method of fabricating FeN/Fe3N nanoparticles with FeN/Fe3N interface exposed on the NP surface for efficient electrochemical CO2 reduction reaction (CO2RR). The FeN/Fe3N interface is populated with Fe−N4 and Fe−N2 coordination sites respectively that show the desired catalysis synergy to enhance the reduction of CO2 to CO. The CO Faraday efficiency reaches 98% at −0.4 V vs. reversible hydrogen electrode, and the FE stays stable from −0.4 to −0.9 V during the 100 h electrolysis time period. This FeN/Fe3N synergy arises from electron transfer from Fe3N to FeN and the preferred CO2 adsorption and reduction to *COOH on FeN. Our study demonstrates a reliable interface control strategy to improve catalytic efficiency of the Fe–N structure for CO2RR.
As promising hydrogen energy carrier, formic acid (HCOOH) plays the indispensable roles in building a complete industry chain of a hydrogen economy. Currently, the biomass upgrading assisted water electrolysis has emerged as an attractive alternative for co-producing green HCOOH and H2 in a cost-effective manner, yet simultaneously affording high current density and Faradaic efficiency (FE) still remains a big challenge. Here we report a ternary NiVRu-layered double hydroxides (LDHs) nanosheet arrays for selective glycerol oxidation and hydrogen evolution catalysis, which yields an industry-level 1 A cm-2 at voltage of 1.933 V, meanwhile showing considerable HCOOH and H2 productivities of 12.5 and 17.9 mmol cm-2 h-1 , with FEs of almost 80% and 96%, respectively. Experimental and theoretical results reveal that the introduced Ru atoms could tune the local electronic structure of Ni-based LDHs, which not only optimizes hydrogen adsorption kinetics for HER, but also reduces the reaction energy barrier for both the conversion of NiII into GOR-active NiШ and carbon-carbon (C-C) bond cleavage. In short, this work highlights the potential of large-scale H2 and HCOOH productions from integrated electrocatalytic system, and provides new insights for designing advanced electrocatalyst for low-cost and sustainable energy conversion. This article is protected by copyright. All rights reserved.
CO2 electroreduction has been considered a promising alternative to simultaneously reduce CO2 emissions and produce value-added products. Among others, the production of formic acid/formate is particularly attractive. Although promising results have already been obtained in the literature, one of the recent approaches to improve the process deals with the use of an alternative reaction at the anode instead of the traditional oxygen evolution reaction (OER). In this context, this work reports, for the first time, the study of the CO2 electroreduction to formate coupled with the electrooxidation of glycerol to high-added value products where both half-reactions operate in a continuous mode with a single pass of the reactants through the electrochemical cell. Interestingly , at the cathode, similar results to those previously reported were obtained, reaching formate concentrations of about 18 g⋅L-1 at a 200 mA⋅cm-2. In addition, at the anode, promising dihydroxyacetone productions of 196 µmol⋅m-2⋅s-1 were simultaneously achieved in the output stream of the anodic compartment. These findings represent a significant step forward for the development and application of the technology.
Electrochemical CO2 conversion is a key technology to promote the production of carbon‐containing molecules, alongside reducing CO2 emissions leading to a closed carbon cycle economy. Over the past decade, the interest to develop selective and active electrochemical devices for electrochemical CO2 reduction emerged. However, most reports employ oxygen evolution reaction as an anodic half‐cell reaction causing the system to suffer from sluggish kinetics with no production of value‐added chemicals. Therefore, this study reports a conceptualized paired electrolyzer for simultaneous anodic and cathodic formate production at high currents. To achieve this, CO2 reduction was coupled with glycerol oxidation: a BiOBr‐modified gas‐diffusion cathode and a NixB on Ni foam anode keep their selectivity for formate in the paired electrolyzer compared to the half‐cell measurements. The paired reactor here reaches a combined Faradaic efficiency for formate of 141 % (45 % anode and 96 % cathode) at a current density of 200 mA cm⁻².
The electro‐reforming of glycerol is an emerging technology of simultaneous hydrogen production and biomass valorization. However, its complex reaction network and limited catalyst tunability restrict the precise steering toward high selectivity. Herein, we incorporated the chelating phenanthrolines into the bulk nickel hydroxide and tuned the electronic properties by installing functional groups, yielding tunable selectivity toward formate (max 92.7 %) and oxalate (max 45.3 %) with almost linear correlation with the Hammett parameters. Further combinatory study of intermediate analysis and various spectroscopic techniques revealed the electronic effect of tailoring the valence band that balances between C−C cleavage and oxidation through the key glycolaldehyde intermediate. A two‐electrode electro‐reforming setup using the 5‐nitro‐1,10‐phenanthroline‐nickel hydroxide catalyst was further established to convert crude glycerol into pure H2 and isolable sodium oxalate with high efficiency.
Electrochemical valorization of surplus biomass-derived feedstocks, such as glycerol, into high-value chemicals offers a sustainable route for utilization of biomass resources and decarbonization of chemical manufacturing; however, glycerol is typically valorized solely via anodic oxidation, with lower-value products such as hydrogen gas generated at the cathode. Here, we establish the efficient cathodic valorization of glycerol to the desirable C3 oxidation products via the electro-Fenton process at a stable NiSe2 cathode, built upon the theoretical understanding and experimental demonstration of the high selectivity and stability of NiSe2 toward acidic H2O2 electrosynthesis. A proof-of-concept linear paired electrochemical process for concurrent valorization of glycerol into the same oxidation products at both NiSe2 cathode and Pt anode achieves high selectivity for value-added C3 products and high glycerol conversion with little external energy input needed, when the electro-Fenton generation of hydroxyl radicals is carefully controlled. This conceptual strategy of linear pairing is generalizable for enabling atom-efficient electro-refinery of diverse biomass-derived feedstocks. Seeking high efficiency in the valorization of biomass-derived feedstocks is a great challenge. Now, a linear paired electrochemical valorization of glycerol to mainly C3 oxidation products is achieved in both compartments by combining the electro-Fenton process at a NiSe2 cathode and the direct oxidation of glycerol at a Pt anode.
CO2 electroreduction has been regarded as an appealing strategy for renewable energy storage. Recently, bismuth (Bi) electrocatalysts have attracted much attention due to their excellent formate selectivity. However, many reported Bi electrocatalysts suffer from low current densities, which are insufficient for industrial applications. To reach the goal of high current CO2 reduction to formate, we fabricate Bi nanosheets (NS) with high activity through edge/terrace control and defect engineering strategy. Bi NS with preferential exposure sites are obtained by topotactic transformation, and the processes are clearly monitored by in-situ Raman and ex-situ X-ray diffraction (XRD). Bi NS-1 with a high fraction of edge sites and defect sites exhibits excellent performance, and the current density is up to ca. 870 mA·cm−2 in the flow cell, far above the industrially applicable level (100 mA·cm−2), with a formate Faradaic efficiency greater than 90%. In-situ Fourier transform infrared (FT-IR) spectra detect *OCHO, and theoretical calculations reveal that the formation energy of *OCHO on edges is lower than that on terraces, while the defects on edges further reduce the free energy changes (ΔG). The differential charge density spatial distributions reveal that the presence of defects on edges causes charge enrichment around the C—H bond, benefiting the stabilization of the *OCHO intermediate, thus remarkably lowering the ΔG.
Electrochemical glycerol oxidation reaction (GOR) is a promising candidate to couple with cathodic reaction, like hydrogen evolution reaction, to produce high‐value product with less energy consumption. Two‐dimensional conjugated metal‐organic frameworks (2D c‐MOFs), comprising square‐planar metal‐coordination motifs (e.g., MO4, M(NH)4, MS4), are notable for their programable active sites, intrinsic charge transport, and excellent stability, making them promising catalyst candidates for GOR. Here, we introduce a novel class of 2D c‐MOFs electrocatalysts, M2[NiPcS8] (M=Co/Ni/Cu), which are synthesized via coordination of octathiolphthalocyaninato nickel (NiPc(SH)8) with various metal centers. Due to a fast kinetic and high activity of CoS4 sites for GOR, the electrocatalytic tests demonstrate that Co2[NiPcS8] supported on carbon paper displays a low GOR potential of 1.35 V vs. RHE at 10 mA cm‐2, significantly reducing the overall water‐electrolysis‐voltage reduction by 0.27 V from oxygen evolution reaction to GOR, thereby outperforming Ni2[NiPcS8] and Cu2[NiPcS8]. Additionally, we have determined that the GOR activity of CoX4 linkage sites varies with different heteroatoms, following an experimentally and theoretically confirmed activity order of CoS4>CoO4>Co(NH)4. The GOR performance of Co2[NiPcS8] not only demonstrate superior performance among non‐noble metal complex, but also provides critical insights on designing high‐performance MOF electrocatalysts upon optimizing the electronic environment of active sites.
The acidic CO2 reduction reaction (CO2RR) offers a promising approach to mitigate CO2 reactant loss and carbonate deposition, which are challenging issues in alkaline or neutral electrolytes. However, the hydrogen evolution reaction (HER) competes in the proton-rich environment near the catalyst surface as a side reaction, reducing the energy efficiency of generating multi-carbon (C2+) products. In this work, we proposed a palladium (Pd) doping strategy in a copper (Cu)-based catalyst to stabilize polarized Cu0-Cu+ sites, thus enhancing the Csingle bondC coupling step during the CO2RR while suppressing HER. At an optimal doping ratio of 6%, the Pd dopants were well dispersed as single atoms without aggregation, allowing for the stabilization of subsurface oxygen (OSub), preserving the polarized Cu0-Cu+ active sites, and reducing the energy barrier of Csingle bondC coupling. The Pd-doped Cu/Cu2O catalyst exhibited a peak Faradaic efficiency (FE) of 64.0% for C2+ products with a corresponding C2+ partial current density of 407.1 mA∙cm−2 at −2.18 V versus a reversible hydrogen electrode, a high CO2 single-pass conversion efficiency (SPCE) of 73.2%, as well as a high electrochemical stability of ∼ 150 h at industrially relevant current densities, thus suggesting a potential approach for tuning the electrocatalytic CO2 performances in acidic environments with higher carbon conversion efficiencies.
Despite the considerable efforts made by the community, the high operation cell voltage of CO2 electrolyzers is still to be decreased to move toward commercialization. This is mostly due to the high energy need of the oxygen evolution reaction (OER), which is the most often used anodic pair for CO2 reduction. In this study, OER was replaced by the electrocatalytic oxidation of glycerol using carbon-supported Pt nanoparticles as an anode catalyst. In parallel, the reduction of CO2 to CO was performed at the Ag cathode catalyst using a membraneless microfluidic flow electrolyzer cell. Several parameters were optimized, starting from the catalyst layer composition (ionomer quality and quantity), through operating conditions (glycerol concentration, applied electrolyte flow rate, etc.), to the applied electrochemical protocol. By identifying the optimal conditions, a 75–85% Faradaic efficiency (FE) toward glycerol oxidation products (oxalate, glycerate, tartronate, lactate, glycolate, and formate) was achieved at 200 mA cm–2 total current density while the cathodic CO formation proceeded with close to 100% FE. With static protocols (potentio- or galvanostatic), a rapid loss of glycerol oxidation activity was observed during the long-term measurements. The anode catalyst was reactivated by applying a dynamic potential step protocol. This allowed the periodic reduction, hence, refreshing of Pt, ensuring stable, continuous operation for 5 h.
The production of formic acid via electrochemical CO2 reduction may serve as a key link for the carbon cycle in the formic acid economy, yet its practical feasibility is largely limited by the quantity and concentration of the product. Here we demonstrate continuous electrochemical CO2 reduction for formic acid production at 2 M at an industrial‐level current densities (i.e., 200 mA cm−2) for 300 h on membrane electrode assembly using scalable lattice‐distorted bismuth catalysts. The optimized catalysts also enable a Faradaic efficiency for formate of 94.2% at 1.16 A·cm−2, reaching a production rate of 21.7 mmol·cm−2·h−1. To assess the practicality of this system, we perform a comprehensive techno‐economic analysis and life cycle assessment, showing that our approach can potentially substitute conventional methyl formate hydrolysis for industrial formic acid production. Furthermore, the resultant formic acid serves as direct fuel for air‐breathing formic acid fuel cells, boasting a power density of 55 mW cm−2 and an exceptional thermal efficiency of 20.1%.
Owing to outstanding performances, nickel‐based electrocatalysts are commonly used in electrochemical alcohol oxidation reactions (AORs), and the active phase is usually vacancy‐rich nickel oxide/hydroxide (NiOxHy) species. However, researchers are not aware of the catalytic role of atom vacancy in AORs. Here, we study vacancy‐induced catalytic mechanisms for AORs on NiOxHy species. As to AORs on oxygen‐vacancy‐poor β‐Ni(OH)2, the only redox mediator is electrooxidation‐induced electrophilic lattice oxygen species, which can only catalyze the dehydrogenation process (e.g., the electrooxidation of primary alcohol to carboxylic acid) instead of the C‐C bond cleavage. Hence, vicinal diol electrooxidation reaction involving the C‐C bond cleavage is not feasible with oxygen‐vacancy‐poor β‐Ni(OH)2. Only through oxygen vacancy‐induced adsorbed oxygen‐mediated mechanism, can oxygen‐vacancy‐rich NiOxHy species catalyze the electrooxidation of vicinal diol to carboxylic acid and formic acid accompanied with the C‐C bond cleavage. Crucially, we examine how vacancies and vacancy‐induced catalytic mechanisms work during AORs on NiOxHy species.
The thermochemical conversion of biomass is potentially vital to meeting global demand for sustainable transport fuels so besides combustion; torrefaction, liquefaction, pyrolysis and gasification are reviewed. The merits and demerits of these processes and examples of industrial applications are evaluated, and two promising avenues for future development are identified. The future of biomass upgrading via thermochemical processing will depend on sector coupling, both within the energy sector and with sectors such as food production. Owing to environmental constraints and the need to maintain food production, the availability of traditional feedstocks for biofuels, such as corn, will be limited in the future. Now given the ambitious targets for sustainable aviation fuel – a higher quality fuel – reserving appropriate feedstocks for aviation fuel will be necessary. Such a policy would open opportunities for the commercial development of the sustainable production of such liquid fuels via liquefaction and pyrolysis. The second avenue of opportunity links to the fact that biomass in the form of wooden pellets has established itself as an essential fuel. In the UK and elsewhere, it is already contributing to the decarbonisation of the electricity grids. So worldwide, a positive future for biomass combustion, aided where appropriate by torrefaction, is envisaged as increasingly crucial for the abatement of greenhouse gas emissions. Alongside battery storage and pumped hydroelectric storage, the contribution of biomass processes, such as torrefaction, to tackling the storage problem arising from the intermittent nature of wind and solar energy has been clarified for the first time.
Electrocatalytic carbon dioxide reduction (CO2RR) is a promising strategy to achieve carbon neutrality. Nevertheless, its practical viability is hindered by the energy-consuming anodic oxygen evolution (OER) process. In recent years, researchers have attempted to break this limitation by some novel anodic OER substitution reactions to improve the overall economic profitability. This article aims to provide a comprehensive review covering the recent development of integrated CO2RR systems with alternative OER oxidation reactions. Starting from the presentation of fundamental considerations of electrolytic configurations, energy efficiency, value-added products and tech-economic analysis for high-performance integrations, the recent innovative anodic reactions are then summarized and thoroughly analyzed including the reactions involving alcohols, biomass, chlorine, water contaminants oxidations and chemicals electrosynthesis, with the focus on electrocatalysts design, electrolyte selection and system configurations. Finally, the current challenges and future perspectives are discussed to achieve the dual goals of sustainability and profitability in an economical and energy-efficient way.
The batch production of high-purity hydrogen is a key problem that restricts the progress of fuel cells and the blueprint for achieving carbon neutrality. Transition-metal chalcogenide heterojunctions exhibit certain activity toward electrochemical overall water splitting (EOWS), but their high-current-density catalytic performances are still unsatisfactory due to the slow kinetic progression (H* or *O → *OOH). Inspired by the "electron pocket" theory, we designed a Ni-Mo bimetallic disulfide interface heterojunction electrocatalyst system (NM-IHJ-V) with high electronic storage capacity around the Fermi level (-0.5 eV, +0.5 eV) (e-DFE), which injects more power into the kinetic progression processes of intermediate species in the EOWS process. Consequently, it achieves a superhigh current density of 2 A cm-2 level for EOWS (only 1.98 V voltage is needed), which is 11.23-fold higher than that of the benchmarked Pt/C//IrO2 (178 mA cm-2@1.98 V), as well as an excellent long-term stability of 200 h. Most strikingly, NM-IHJ-V can efficiently produce hydrogen at currents up to 5 A. Our proposed strategy of constructing catalysts to produce hydrogen at superhigh current density through the electron pocket theory will supply valuable insights for the designing other catalytic systems.
Valorization of biomass-derived feedstocks for the supply of high-value chemicals, clean fuel and electricity is gaining importance in the context of the circular economy. In particular, raw chemicals can be produced by electrocatalytic, photocatalytic and photoelectrochemical oxidation of glycerol, a by-product of biodiesel manufacturing. Nonetheless, controlling the selectivity of the oxidation of glycerol, a C3 compound, is challenging. Indeed, a wide range of C1 to C3 products containing carbonyl or carboxyl groups are produced, thus limiting the development of catalytic glycerol transformation. Here, we review electrooxidation, photooxidation and photoelectrooxidation of glycerol with emphasis on sustainability, and selectivity in catalytic systems. We also discuss co-electrolysis and fuel cells that present promising strategies involving glycerol oxidation.
The conventional anodic oxygen evolution (OER) in electrochemical CO2 reduction (CO2R) needs to be replaced as it accounts for a major share in energy consumption while being a product of little to no value. In this work, we replace OER by glycerol oxidation reaction (GOR) to synthesize products such as formate, lactate and glycolate. Hereby, for the first time, GOR was successfully paired with cathodic CO2R to formate in a flow reactor at a significant current density of 50 mA/cm2 producing value added anode products with a simultaneously reduced cell voltage. Using a porous platinum anode, GOR reduced the anode potential as well as cell potential by ∼1 V compared to OER. We report an anodic Faraday efficiency (FE) of 30% to ∼53% for liquid products, of which lactate dominates. The structure of the electrode has a significant impact on the dominant product as mainly formate is synthesized on a planar electrode, where the cummulated FE for all liquid products is up to 76%. The concurrent FE to formate at cathode and anode reached a values of up to 74% and 30% respectively and 66% and 76%, respectively, considering all value-added products. By successfully pairing GOR with CO2R in a flow cell reactor, this work marks an important step towards energy-efficient and economically viable processes.
The development of an efficient and low-cost electrocatalyst for oxygen evolution reaction (OER) is the key to improving the overall efficiency of water electrolysis. Here, we report the design of a three-dimensional (3-D) heterostructured Ni9S8/Ni3S2 precatalyst composed of unstable Ni9S8 and inert Ni3S2 components, which undergoes in situ electrochemical activation to generate an amorphous-NiOOH/Ni3S2 heterostructured catalyst. In situ Raman spectroscopy combined with ex situ characterizations, such as X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy, reveals that during the activation, Ni9S8 loses the sulfur element to form nickel oxides and eventually transforms to amorphous NiOOH at O2-evolving potentials, while the Ni3S2 component is rather inert that its majority in the bulk remains, thus forming a 3-D congee-like NiOOH/Ni3S2 heterostructure with the Ni3S2 crystalline particles randomly dispersed among amorphous NiOOH species. Unlike the sparse heterostructure that consists of a layer of NiOOH on top of Ni3S2, our unique congee-like NiOOH/Ni3S2 heterostructure provides plentiful reactive amorphous-crystalline interfacial sites. Moreover, the partial electron transfer between the NiOOH and remaining Ni3S2, benefiting from their dense interfacial sites, contributes to a higher valence state of the Ni3+ active centers in NiOOH, hence optimizing the adsorption of OER intermediates. Density functional theory calculations further disclose that the electronic structure regulation not only optimizes the Gibbs free energy of intermediate adsorption but also tunes the OH* absorption behavior to be exothermic, elucidating the spontaneous occurrence of OH* absorption and hence improves the OER. Therefore, a low overpotential of only 197 mV at an O2-evolving current density of 10 mA/cm2, a small Tafel slope of 38.8 mV/dec, and good stability are achieved on the amorphous-NiOOH/crystalline-Ni3S2 heterostructured catalyst.
Formates are promising salts for hydrogen storage. They can be catalytically converted to bicarbonate at near-ambient conditions, and regenerated under moderate pressure for H2 uptake. Moreover, the system is completely safe, non-toxic, and easy to handle. Up to date, a few heterogeneous catalytic systems have been proposed to carry this transformation. However, many criticisms still have to be addressed, including reaction kinetics for high power applications, stability, cyclability, and supersaturated solutions to increase energetic density. In this work, a critical review of the state of art of such system is presented, highlighting theoretical limitations and applicative shortcomings, and giving perspective on critical issues to be addressed in future research. Despite the actual bottlenecks, the system is still scarcely explored and there is promising room for improvement. State-of-the-art catalytic systems could provide 72% energetic efficiency, that could be improved up to 90%.
The Deoxydehydration (DODH) of glycerol to allyl alcohol was studied over ceria-supported rhenium oxide catalyst. Mesoporous ceria materials were synthetized via a nanocasting process using SiO2 and activated carbon as hard templates. The as-obtained ceria supports were impregnated with 2.5-10 wt.% ReOx. and applied in the DODH reaction of glycerol to allyl alcohol at 175°C in batch conditions using 2-hexanol as solvent and hydrogen donor. As the characterisations revealed that the template removal was a critical step in the synthesis of the mesostructured ceria via the nanocasting method, the influence of the presence of the hard template was studied in detail by comparison to commercial ceria supports. The catalyst based on the nanocasting ceria showed higher performance of up to 88% yield in allyl alcohol and was reusable for 3 cycles without reactivation step. No evidence of leaching was observed via hot filtration test. The characterisation of the catalyst by XPS revealed the presence of Re⁴⁺ species after test, which led us propose that two redox couples, namely Re⁷⁺/Re⁵⁺ and Re⁶⁺/Re⁴⁺, are involved during DODH of glycerol to allyl alcohol, which was further confirmed by DFT calculations.
Glycerol is one of the most important biomass-based platform molecules, massively produced as a by-product in the biodiesel industry. Its high purification cost from the crude glycerol raw material limits its application and demands new strategies for valorization. Compared to the conventional thermocatalytic strategies, the electrocatalytic strategies can not only enable the selective conversion at mild conditions but also pair up the cathodic reactions for the co-production with higher efficiencies. In this review, we summarize the recent advances of catalyst designs and mechanistic understandings for the electrocatalytic glycerol oxidation (GOR), and aim to provide an overview of the GOR process and the intrinsic structural-activity correlation for inspiring future work in this field. The review is dissected into three sections. We will first introduce the recent efforts of designing more efficient and selective catalysts for GOR, especially toward the production of value-added products. Then, we will summarize the current understandings about the reaction network based on the ex-situ and in-situ spectroscopic studies as well as the theoretical works. Lastly, we will select some representative examples of creating real electrochemical devices for the valorization of glycerol. By summarizing these previous efforts, we will provide our vision of future directions in the field of GOR toward real applications.
Generation of H2 and O2 by electrochemical water splitting is a sustainable strategy for a greener society. Recently, attention has been paid to designing 3D porous electrodes using Fe, Co, Ni, Cu, and C foam materials as substrates to obtain larger current densities (>500 mA cm⁻²) for industrial applications. However, oversimplification of the experimental and quantitative processes for foam electrodes has made it difficult to fully understand the electrocatalytic nature and develop the proper catalysts. Hence, an objective evaluation of the electrocatalytic activity is necessary and problems associated with foam materials must be better understood, including the impact of the surface area, current density normalization, electrode thickness, electrocatalytic mass, active materials, and electrochemical measurements.