Stephen J. Skinner

• PhD
• Professor at Imperial College London

Understanding and controlling the interfaces between different materials is crucial for developing solid oxide cells (SOCs) with both high performance and durability for low-temperature operation (<700 °C). Current research focuses on evaluating microstructural designs and composite material interactions to optimize SOC performance. Nanocomposite h...

Piezoelectric materials are indispensable in electromechanical actuators, which require a large electrostrain with a fast and precise response. By designing a chemopiezoelectric effect, we developed an approach to achieve a high electrostrain of 1.9% under −3 kV mm⁻¹, at 1 Hz, corresponding to an effective piezoelectric coefficient of >6,300 pm V⁻¹...

Protonic ceramic electrochemical cells (PCECs) can operate at intermediate temperatures (450° to 600°C) for power generation and hydrogen production. However, the operating temperature is still too high to revolutionize ceramic electrochemical cell technology. Lowering the operating temperature to <450°C will enable a wider material choice and redu...

LaNb0.84W0.16O4+δ and LaNb0.84Mo0.16O4+δ produced via a solid-state reaction route exhibited excellent phase stability after annealing under 5%-H2/N2 atmosphere at 800 °C, confirming their potential for application in reducing environments, such...

Metal exsolution reactions can be driven in fuel electrode materials under the reducing operation conditions of solid oxide cells. The process enables the synthesis of nanostructured catalysts based on the release of a fraction of reducible dopants from a perovskite host to its’ surface and the subsequent nucleation of finely dispersed oxide-suppor...

Exsolution reactions enable the synthesis of oxide-supported metal nanoparticles, which are desirable as catalysts in green energy conversion technologies. It is crucial to precisely tailor the nanoparticle characteristics to optimize the catalysts’ functionality, and to maintain the catalytic performance under operation conditions. We use chemical...

Grain boundary (GB) mass transport, and chemistry exert a pronounced influence on both the performance and stability of electrodes for solid oxide electrochemical cells. Lanthanum strontium cobalt ferrite (LSCF6428) is applied as a model mixed ionic and electronic conducting (MIEC) perovskite oxide. The cation‐vacancy distribution at the GBs is stu...

Halide solid electrolytes do not currently display ionic conductivities suitable for high-power all-solid-state batteries. We explore the model system A2ZrCl6 (A = Li, Na, Cu, Ag) to understand the fundamental role that A-site chemistry plays on fast ion transport. Having synthesised the previously unknown Ag2ZrCl6 we reveal high room temperature i...

Arsenite, As(III), is a highly toxic form of arsenic that poses a significant risk to human health if present in drinking water. Oxidation of As(III) to the less toxic As(V) using TiO2 as photocatalyst is an attractive solution in water treatment applications but challenged the high bandgap energy. In this study, we investigate the potential of dop...

Exsolution, an innovative method for fabricating perovskite-based oxides decorated with metal nanoparticles, has garnered significant interest in the fields of catalyst fabrication and electrochemical devices. Although dopant exsolution from single perovskite structures has been extensively studied, the exsolution behaviour of double perovskite str...

The implementation of nanocomposite materials as electrode layers represents a potential turning point for next-generation of solid oxide cells in order to reduce the use of critical raw materials. However, the substitution of bulk electrode materials by thin films is still under debate especially due to the uncertainty about their performance and...

Increasing densities of reaction sites for gaseous reactants in solid oxide electrochemical reactors (SOERs), is a key strategy for achieving enhanced performance in either fuel cell or electrolysis modes. Fabrication of 3D structured components in SOERs can enhance those densities of reaction sites, which is achieved by 3D inkjet printing with hig...

Halide solid electrolytes do not currently display ionic conductivities suitable for high-power all-solid-state batteries. We explore the model system A 2 ZrCl 6 (A = Li, Na, Cu, Ag) to understand the fundamental role that A-site chemistry plays on fast ion transport. Having synthesised Ag 2 ZrCl 6 for the first time we reveal exceptional room temp...

Exsolution reactions enable the synthesis of oxide-supported metal nanoparticles, desir- able as catalysts in green energy conversion technologies. It is crucial to precisely tai- lor the nanoparticle characteristics to tune the catalysts’ functionality, and to maintain the catalytic performance under operation conditions. We use chemical (co)-dopi...

Interest in solid-state sodium-ion batteries (SSIBs) have resurged remarkably as a means of diversification in energy storage devices to address climate issues and further propelled by the movement of ‘Beyond-Li’. State of the art SSIBs not only offer energy security and sustainability but also comparable power and energy densities to their counter...

Development of next-generation electrochemical devices, such as solid oxide cells, requires control of the charge transfer processes across key interfaces. Structural strain at electrolyte:electrode interfaces could potentially alter the devices’ charge transport properties, therefore understanding the structural behavior of electrode surfaces unde...

A fundamental understanding of the electrochemical reactions and surface chemistry at the solid–gas interface in situ and operando is critical for electrode materials applied in electrochemical and catalytic applications. Here, the surface reactions and surface composition of a model of mixed ionic and electronic conducting (MIEC) perovskite oxide,...

The appropriate orientation of antibodies on the graphene surface is critical for the high performance of graphene biosensors. In this paper, we show that a predominantly vertical orientation of antibodies to the graphene surface can be achieved by functionalizing the surface with tetrakis (4-carboxyphenyl) porphyrin (TCPP). We used this method to...

Nanostructured La 0.6 Sr 0.4 CoO 3-δ (LSC) thin film electrodes exhibit exceptionally high oxygen surface exchange properties, surpassing those of conventional microscale electrode structures, which are desirable for application in solid oxide cells (SOC) [1-2]. On the other hand, the LSC nanostructures also tend to undergo significant morphologica...

A series of higher-order Ruddlesden-Popper phase materials – La 3 PrNi 3 O 9.76 (L3P1N3), La 2 Pr 2 Ni 3 O 9.65 (L2P2N3) and LaPr 3 Ni 3 O 9.76 (L1P3N3) – were synthesised and investigated by neutron powder diffraction to understand the oxygen defect structure and propose possible pathways for oxygen transport in these materials. Further compliment...

Storage of purified hydrogen is one of the central challenges in addressing climate change and reducing our reliance on fossil fuels for energy conversion and storage, and therefore there is a global surge in research and development concerning hydrogen purification and storage. In this regard, we are studying proton conduction in solid oxide mater...

The surface electrochemical catalysis reaction is complex due to the unpredictable surface morphology and severe reaction environment, especially for cathodes in proton conducting solid oxide fuel cells (H-SOFCs) where water vapor is generated and evaporated at a high operating temperature. The first-generation cathode materials (La x Sr 1-x MO 3-δ...

The mixed-ionic electronic conduction (MIEC) of gadolinium doped ceria (CGO) under reduced oxygen conditions makes it an excellent fuel electrode material for SOFC/SOEC applications. As part of a composite electrode (Ni/CGO), the nickel phase offers a fast electronic conduction pathway to the current collector and may act as an electrocatalyst at t...

A composite electrode composed of Pr4Ni3O10±δ - Ce0.75Gd0.1Pr0.15O2−δ (50 wt. % - 50 wt. %) was thoroughly investigated in terms of the electrochemical performance as a function of microstructure. The electrochemical performance was characterized by electrochemical impedance spectroscopy and the microstructures, characterized by focused ion beam-sc...

Single phase La1−xGdxNb0.9Mo0.1O4.05 (x = 0, 0.20, 0.40, 0.50, 0.60, 0.80 and 1.00) has been synthesized by a solid state reaction route. The crystal structures of all samples were investigated by high temperature X-ray diffraction. Both LaNb0.9Mo0.1O4.05 and La0.8Gd0.2Nb0.9Mo0.1O4.05 were found to possess modulated crystal structures at room tempe...

Understanding the charge transfer processes at solid oxide fuel cell (SOFC) electrodes is critical to designing more efficient and robust materials. Activation losses at SOFC electrodes have been widely attributed to the ambipolar migration of charges at the mixed ionic–electronic conductor–gas interface. Empirical Butler–Volmer kinetics based on t...

A series of Ruddlesden-Popper phase materials – La3PrNi3O10-d, La2Pr2Ni3O10-d and LaPr3Ni3O10-d – were synthesised and investigated by neutron powder diffraction to understand the oxygen defect structure. The thermal expansion coefficient was calculated for all compositions and was found to be in the range of 13.0 - 13.4 × 10-6 ̊C-1, which is compa...

Computational simulation, based on Density Functional Theory (DFT), was carried out to develop a more powerful cathode material, La 0.35 Bi 0.15 Sr 0.5 FeO 3-δ (LBSF), based on a first-generation cathode material, La 0.5 Sr 0.5 FeO 3-δ (LSF) for use in proton-conducting solid oxide fuel cells (H-SOFCs). The calculation results show that the Bi subs...

Nanostructured La 0.6 Sr 0.4 CoO 3- δ (LSC) thin film electrodes exhibit exceptionally high oxygen surface exchange properties, surpassing those of conventional microscale electrode structures, which are desirable for application in solid oxide cells (SOCs). Here, towards the goal of improving the long-term stability of electrochemical performance...

A series of higher-order Ruddlesden–Popper phase materials – La3PrNi3O10−d, La2Pr2Ni3O10−d and LaPr3Ni3O10−d – were synthesised and investigated by neutron powder diffraction to understand the oxygen defect structure and propose possible pathways for oxygen transport in these materials. Further complimentary DFT calculations of the materials were p...

Electrochemical impedance spectroscopy (EIS) is a powerful tool in characterisation of processes in electrochemical systems, allowing us to elucidate the resistance and characteristic frequency of physical properties such as reaction and transport rates. The essence of EIS is the relationship between current and potential at a given frequency. Howe...

Understanding the interfacial dynamics of batteries is crucial to control degradation and increase electrochemical performance and cycling life. If the chemical potential of a negative electrode material lies outside of the stability window of an electrolyte (either solid or liquid), a decomposition layer (interphase) will form at the interface. To...

To harness all of the benefits of solid-state battery (SSB) architectures in terms of energy density, their negative electrode should be an alkali metal. However, the high chemical potential of alkali metals makes them prone to reduce most solid electrolytes (SE), resulting in a decomposition layer called an interphase at the metal|SE interface. Qu...

The effect of operating conditions on the surface composition and evolution of (La 0.8 Sr 0.2 ) 0.95 Cr 0.5 Fe 0.5 O 3-δ (LSCrF8255) as a model perovskite oxide was investigated. LSCrF8255 pellets were annealed under dry oxygen (pO 2 =...

Understanding the interfacial dynamics of batteries is crucial to control degradation and increase electrochemical performance and cycling life. If the chemical potential of a negative electrode material lies outside of the stability window of an electrolyte (either solid or liquid), a decomposition layer (interphase) will form at the interface. To...

To harness all the benefits of solid-state battery (SSB) architectures in terms of energy density, their negative electrode should be an alkali metal. However, the high chemical potential of alkali metals makes them prone to reduce most solid electrolytes (SE), resulting in a decomposition layer called an interphase at the metal|SE interface. Quant...

Activation losses at solid oxide fuel cell (SOFC) electrodes have been widely attributed to charge transfer at the electrode surface. The electrostatic nature of electrode-gas interactions allows us to study these phenomena by simulating an electric field across the electrode-gas interface, where we are able to describe the activation overpotential...

Chemical looping processes based on multiple-step reduction and oxidation of metal oxides hold great promise for a variety of energy applications, such as CO 2 capture and conversion, gas separation, energy storage, and redox catalytic processes. Copper-based mixed oxides are one of the most promising candidate materials with a high oxygen storage...

Activation losses at solid oxide-fuel cell (SOFC) electrodes have been widely attributed to charge transfer at the electrode surface. The electrostatic nature of electrode-gas interactions allows us to study these phenomena by simulating an electric field across the electrode-gas interface, where we are able to describe the activation overpotential...

Thermochemical redox reactors store concentrated solar power by thermally inducing an oxygen deficiency within a metal oxide structure. The metal oxide’s affinity for reoxidation allows it to facilitate the splitting of H 2 O or CO 2 to produce H 2 or CO for syngas formation.[1] Typically, high temperatures (>1400 °C) are used to drive the reductio...

Storage of purified hydrogen is one of the central challenges in addressing climate change and reducing our reliance on fossil fuels for energy conversion and storage, and therefore there is a global surge in research and development concerning hydrogen purification and storage. In this regard, we are studying proton conduction in solid oxide mater...

Understanding the interfacial dynamics of batteries is crucial to control degradation and increase electrochemical performance and cycling life. If the chemical potential of a negative electrode material lies outside of the stability window of an electrolyte (either solid or liquid), a decomposition layer (interphase) will form at the interface. To...

Activation losses at solid oxide-fuel cell (SOFC) electrodes have been widely attributed to charge transfer at the electrode surface. The electrostatic nature of electrode-gas interactions allows us to study these phenomena by simulating an electric field across the electrode-gas interface, where we are able to describe the activation overpotential...

To harness all the benefits of solid-state battery (SSB) architectures in terms of energy density, their negative electrode should be an alkali metal. However, the high chemical potential of alkali metals make them prone to reduce most solid electrolytes (SE), resulting in a decomposition layer called an interphase at the metal|SE interface. Quanti...

Sodium–bismuth–titanate (NBT) has recently been shown to contain high levels of oxide ion conductivity. Here we report the effect of A‐site monovalent ions, M⁺ = K⁺ and Li⁺, on the electrical conductivity of NBT. The partial replacement of Bi³⁺ with monovalent ions improved the ionic conductivity by over one order of magnitude without an apparent c...

The use of perovskite materials for thermochemical energy storage has been gaining momentum in recent years due to their ability to topotactically exchange large volumes of oxygen, and their chemical and structural flexibility which results in interesting transport and catalytic properties. B-site substituted SrCoO3-δ derivatives have previously be...

Exsolution of stable metallic nanoparticles for use as efficient electrocatalysts has been of increasing interest for a range of energy technologies. Typically, exsolved nanoparticles show higher thermal and coarsening stability compared to conventionally deposited catalysts. Here, A‐site deficient double perovskite oxides, La2‐xNiRuO6‐δ (x = 0.1 a...

In the last couple of decades, researchers have been working on Ruddlesden-Popper phases to realise them as components of solid oxide cells. Ruddlesden-Popper phase materials have been particularly proposed as materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). As such a sizeable literature was produced on Ruddlesden-Popper ph...

Stephen Skinner, Viola Birss, Jennifer Rupp and Roger De Souza introduce the Journal of Materials Chemistry A special issue in honour of Prof. John Kilner’s 75th birthday.

The BCZY perovskite was studied by NDP, QENS and TOF-SIMS techniques, focusing on the application of this material as a potential PC-SOFC electrolyte.

Non-equilibrium thermodynamics describe the current-voltage characteristics of electrochemical devices. For conventional electrode-electrolyte interfaces, the local activation overpotential is used to describe the electrostatic potential step between the two materials as...

The determination of reaction rates for the photocatalytic oxidation (PCO) of arsenite (As(III)) using TiO 2 under UV radiation is challenging due to the numerous experimental processes. This includes chemical processes running simultaneously with PCO (e.g. adsorption of arsenic species, direct UV photolysis of As(III)) and the analytical approach...

Single-phase Hf2Al4C5 ternary carbide was fabricated from Hf/Al/C powder mixtures by pressure assisted sintering techniques such as hot pressing and spark plasma sintering at 1900 °C for 3h and 10min, respectively. XRD confirmed that the ternary carbide started to form at temperatures as low as 1500°C and with total formation of Hf2Al4C5 after reac...

The catalytic and transport properties of mixed ionic-electronic conducting (MIEC) electrodes for solid oxide fuel cells (SOCs) are well documented and utilised, yet poorly understood. In the current study, a novel kinetic framework for the electrochemical behaviour of hydrogen at the MIEC-gas interface will be discussed for three parallel treatmen...

Inorganic perovskites exhibit many important physical properties such as ferroelectricity, magnetoresistance and superconductivity as well their importance as energy materials. Many of the most important energy materials are inorganic perovskites and find application in batteries, fuel cells, photocatalysts, catalysis, thermoelectrics and solar the...

The magnitude of the electrostatic potential at the surface of a mixed ionic-electronic conducting (MIEC) solid-oxide cell (SOC) electrode is dependent on the intrinsic dipole moment of adsorbed gas species. Using density functional theory, we have investigated the electrostatic nature of hydroxyl adsorbates and the kinetics of electron transfer in...

The local activation overpotential describes the electrostatic potential shift away from equilibrium at an electrode/electrolyte interface. This electrostatic potential is not entirely satisfactory for describing the reaction kinetics of a mixed ionic-electronic conducting (MIEC) solid-oxide cell (SOC) electrode where charge transfer occurs at the...

The potential of calcium-doped layered perovskite compounds, BaNd1-x Ca x InO4-x/2 (where x is the excess Ca content), as protonic conductors was experimentally investigated. The acceptor-doped ceramics exhibit improved total conductivities that were 1-2 orders of magnitude higher than those of the pristine material, BaNdInO4. The highest total co...

Oxide-ion conductors are important in various applications such as solid-oxide fuel cells. Although zirconia-based materials are widely utilized, there remains a strong motivation to discover electrolyte materials with higher conductivity that lowers the working temperature of fuel cells, reducing cost. Oxide-ion conductors with hexagonal perovskit...

Substituted SrCoO 3 perovskites have been proposed as promising mixed ionic electronic conductors for a range of applications including intermediate temperature solid oxide fuel cells (IT-SOFC), electrolysers and thermochemical water spliting...

Innovative concepts for novel electrode structures have been actively pursued over recent years to achieve both superior electrochemical performance as well as long-term stability for the development of solid oxide...

Thin-films deposited by Pulsed Laser Deposition (PLD) have enabled the fabrication of cathodes for solid oxide cells (SOC) to possess various microstructures, crystalline states and surface chemistry. These films are often subjected to various processing and thermal treatments which influence the chemical activity and stability of the films. Here,...

Limited oxygen surface exchange for oxygen transport membrane (OTM) material in humid atmosphere, correlated with Sr surface segregation identified using isotopic exchange and mass spectrometry.

Note: The Special Awards Committee of the ASME (American Society of Mechanical Engineers) has awarded Daniel Castillo the Warren M. Rohsenow Award at the ASME Turbo Expo 2020. The Prize is handed to the best presentation at a technical session on heat transfer in gas turbine systems. The poster’s theme is about a new temperature measurement techn...

Electrodes in solid-state energy devices are subjected to a variety of thermal treatments, from film processing to device operation at high temperatures. All these treatments influence the chemical activity and stability of the films, as the thermally induced chemical restructuring shapes the microstructure and the morphology. Here, we investigate...

Many novel composite materials have been recently developed for water treatment applications, with the aim of achieving multifunctional behaviour, e.g. combining adsorption with light-driven remediation. The application of surface complexation models (SCM) is important to understand how adsorption changes as a function of pH, ionic strength and the...

Solid oxide fuel cells typically operate at temperatures near 800 °C. One obstacle to reducing this temperature is finding a high-performance cathode for lower temperatures. La2NiO4+δ (LNO) has shown promise as a good material as a cathode being a well-known mixed electronic and ionic conductor. However, increasing the surface exchange in LNO is im...

Pr4Ni3O10 is a promising air electrode for solid oxide fuel cells and electrolysers with comparable performance to Pr2NiO4+δ but with improved thermodynamic stability at a cell operating temperature of 600 °C–800 °C. To fully understand and integrate Pr4Ni3O10 into commercial devices there are several aspects that remain to be addressed. This study...

Systematic studies of the air electrode and full solid oxide fuel cell performance of La3PrNi3O9.76, and La2Pr2Ni3O9.65 n = 3 Ruddlesden–Popper phases are reported. These phases were found to adopt orthorhombic symmetry with a decrease in lattice parameters on increasing Pr content, consistent with the solid solution series end members. From electr...

We report investigation of phonons and oxygen diffusion in Bi2O3 and (Bi0.7Y0.3)2O3. The phonon spectra have been measured in Bi2O3 at high temperatures up to 1083 K using inelastic neutron scattering. Ab-initio calculations have been used to compute the individual contributions of the constituent atoms in Bi2O3 and (Bi0.7Y0.3)2O3 to the total phon...

Significant interest has been directed towards the development of high performance air electrodes for solid oxide electrolysis cells, with a wide variety of potential materials considered. Much of the effort has been directed towards modification of conventional solid oxide fuel cell electrode materials, such as La 1-x Sr x Co 1-y Fe y O 3-d (LSCF)...

Hyper-stoichiometric CeNbO4+d phases demonstrate remarkable oxygen diffusivity and provide an interesting structural template for oxygen ion conductors. Previously, we have reported the room temperature structure of the incommensurate modulated LaNb0.88W0.12O4+d, a structural analogue of CeNbO4+d, and suggested that it is a pure oxygen ion conducto...

We report investigation of phonons and oxygen diffusion in Bi2O3 and (Bi0.7Y0.3)2O3. The phonon spectra have been measured in Bi2O3 at high temperatures up to 1083 K using inelastic neutron scattering. Ab-initio calculations have been used to compute the individual contributions of the constituent atoms in Bi2O3 and (Bi0.7Y0.3)2O3 to the total phon...

Understanding the effects of lattice strain on oxygen surface and diffusion kinetics in oxides is a controversial subject that is critical for developing efficient energy storage and conversion materials. In this work, high‐quality epitaxial thin films of the model perovskite La0.5Sr0.5Mn0.5Co0.5O3−δ (LSMC), under compressive or tensile strain, are...

Lower operating temperatures (≤ 650 °C) of solid oxide fuel cells (SOFCs) are sought in order to decrease the system costs and improve material compatibility and durability issues. Here, we report A-site deficient (La0.7Sr0.3)0.95(Co0.2Fe0.8)O3−δ (LSCF) perovskite film as a potential high-performance cathode with microstructural details at the nano...

In developing a new compositae air electrode for Solid Oxide Cells (SOCs) it is essential to fully understand the phase chemistry of all components. Ruddlesden-Popper type electrodes such as Pr2NiO4+δ have previously been proposed as attractive alternatives to conventional La0·6Sr0·4Fe0·8Co0·2O3-δ/Ce1-xGdxO2-δ compositae air electrodes for both fue...

Lower operating temperatures (≤ 650 °C) of solid oxide fuel cells (SOFCs) are sought in order to decrease the system costs and improve material compatibility and durability issues. Here, we report A-site deficient (La0.7Sr0.3)0.95(Co0.2Fe0.8)O3−δ (LSCF) perovskite film as a potential high-performance cathode with microstructural details at the nano...

In solid oxide electrochemical cells the critical processes of fuel oxidation and oxygen reduction occur at surfaces, and ultimately define the performance of the devices. Understanding how these process occur and the role of defects such as dislocations and grain boundaries in these charge transfer processes, and the effect of cation segregation o...