Oxygen Evolution Reaction Conditions Research Articles

Rapid reconstruction of nickel iron hydrogen cyanamide with in-situ produced proton acceptor for efficient oxygen evolution

Metal oxyhydroxide (MOOH) through irreversible reconstructed fabrication from transition metal compounds are highly efficient oxygen evolution reaction (OER) electrocatalysts but face limits from adsorption energy scaling relationship and sluggish deprotonation kinetics. Herein, we present Fe-doped nickel hydrogen cyanamide (Ni0.8Fe0.2-HC), which is rapidly surface reconstructed into Ni0.8Fe0.2(OOH)-HC after OER. In-situ Raman spectroscopy and density functional theory (DFT) calculations, revealed that under OER conditions, -HNCN- converts into -NCN- ligand incorporating its abundant and uniform distribution across the active sites. DFT calculations further indicate that Fe predominantly acts as the active site, with -NCN- ligands contribute to the OER by facilitating the deprotonation of *OH in the rate-determining step (RDS), acting effectively as proton acceptor. The ensemble effect between Fe and -NCN- ligand forms the foundation of the exceptional electrocatalytic performance of Ni0.8Fe0.2(OOH)-HC (190 mV at 20 mA·cm−2). This discovery offers insights for designing innovative MOOH pre-catalysts to enhance OER efficiency.

Modulating Carrier Oxygen Vacancies to Enhance Strong Oxide‐Support Interaction in IrO2/Nb2O5‐x Catalysts for Promoting Acidic Oxygen Evolution Reaction

AbstractGiven the pronounced dissolution of electrocatalysts in acidic environments, the quest for effective oxygen evolution reaction (OER) electrocatalysts suitable for proton exchange membrane (PEM) water electrolyzers persists as a formidable challenge. In this investigation, catalysts are synthesized by creating oxygen vacancies within various metal oxides (Nb2O5‐x, Ta2O5‐x, ZrO2‐x, TiO2‐x) through plasma‐assisted method, thereby facilitating the immobilization of IrO2 onto these defect‐rich surfaces. The findings unveil that IrO2/Nb2O5‐x manifests reduced overpotentials during acidic OER, achieving an overpotential down to 225 mV@10 mA cm−2, coupled with outstanding durability at multicurrent densities exceeding 200 h, attributed to strong oxide‐support interaction (SOSI) between the IrO2 catalyst and Nb2O5‐x substrate. Density functional theory (DFT) computations uncover intensified binding affinities between IrO2 and Nb2O5‐x, thus modulating the central energy levels of Ir's d orbitals toward favorable OER conditions, consequently bolstering the electrocatalytic activity and stability of the composite catalyst. Furthermore, employing IrO2/Nb2O5‐x as a PEM electrolyzer anode enables consistent operation at 1000 mA cm−2 for 200 h, with an Ir content of only 0.2852 mg cm−2 and an energy consumption of 4.34 kWh Nm−3 H2. This achievement substantially lowers the cost of hydrogen production to US$ 0.96 per kilogram, underscoring its potential for practical applications.

Molecular O2 Dimers and Lattice Instability in a Perovskite Electrocatalyst.

Structural degradation of oxide electrodes during the electrocatalytic oxygen evolution reaction (OER) is a major challenge in water electrolysis. Although the OER is known to induce changes in the surface layer, little is known about its effect on the bulk of the electrocatalyst and its overall phase stability. Here, we show that under OER conditions, a highly active SrCoO3-x electrocatalyst develops bulk lattice instability, which results in the formation of molecular O2 dimers inside the bulk and nanoscale amorphization induced via chemo-mechanical coupling. Using high-resolution resonant inelastic X-ray scattering and first-principles calculations, we unveil the potential-dependent evolution of lattice oxygen inside the perovskite and demonstrate that O2 dimers are stable in a densely packed crystal lattice, thus challenging the assumption that O2 dimers require sufficient interatomic spacing. We also show that the energy cost of local atomic rearrangements in SrCoO3-x becomes very low under the OER conditions, leading to an unusual amorphization under intercalation-induced stress. As a result, we propose that the amorphization energy can be calculated from the first principles and can be used to assess the stability of electrocatalysts. Our study demonstrates that extreme oxidation of electrocatalysts under OER can intrinsically destabilize the lattice and result in bulk anion redox and disorder, suggesting why some oxide materials are unstable and develop a thick amorphous layer under water electrolysis conditions.

Intercalation-Induced Irreversible Lattice Distortion in Layered Double Hydroxides.

Inducing strain in the lattice effectively enhances the intrinsic activity of electrocatalysts by shifting the metal's d-band center and tuning the binding energy of reaction intermediates. NiFe-layered double hydroxides (NiFe LDHs) are promising electrocatalysts for the oxygen evolution reaction (OER) due to their cost-effectiveness and high catalytic activity. The distorted β-NiOOH phase produced by the Jahn-Teller effect under the oxidation polarization is known to exhibit superior catalytic activity, but it eventually transforms to the undistorted γ-NiOOH phase during the OER process. Such a reversible lattice distortion limits the OER activity. In this study, we propose a facile boron tungstate (BWO) anion intercalation method to induce irreversible lattice distortion in NiFe LDHs, leading to significantly enhanced OER activity. Strong interactions with BWO anions induce significant stress on the LDH's metal-hydroxide slab, leading to an expansion of metal-oxygen bonds and subsequent lattice distortion. In situ Raman spectroscopy revealed that lattice-distorted NiFe LDHs (D-NiFe LDHs) stabilize the β-NiOOH phase under the OER conditions. Consequently, D-NiFe LDHs exhibited low OER overpotentials (209 and 276 mV for 10 and 500 mA cm-2, respectively), along with a modest Tafel slope (33.4 mV dec-1). Moreover, D-NiFe LDHs demonstrated excellent stability at 500 mA cm-2 for 50 h, indicating that the lattice distortion of the LDHs is irreversible. The intercalation-induced lattice strain reported in this study can provide a general strategy to enhance the activity of electrocatalysts.

Structural Instability of NiFe‐Layered Double Hydroxide Nanosheets during Water Oxidation Operation

AbstractNiFe‐layered double hydroxide (NiFe‐LDH) stands out as a promising electrocatalyst for the oxygen evolution reaction (OER), but the structural transformations under OER conditions are not well understood. The structural evolution of highly crystalline NiFe‐LDH on nickel foam during OER testing in 1 M KOH solution was analyzed using IR, Raman, XRD, XPS techniques, and DFT calculations. Instability of interlayer species within the NiFe‐LDH, including protons, anions, and water molecules, was found to cause the crystal structure to undergo expansion or contraction during OER operation, decreasing crystallinity and roughening the LDH surface. This dynamic structural evolution is crucial for determining OER activity, and it was observed that surface structural changes of the LDH, along with Fe content, jointly determined the degree of change in its OER activity. Our findings provide insights into designing active water‐splitting electrocatalysts and highlight the relationship between OER activity and the structure of NiFe‐LDH.

First-principles study on the Te/Po doped SrTiO3 (100) surface for photocatalytic overall water splitting to produce hydrogen

The (100) surface of SrTiO3 is inefficient for solar photocatalytic performance because its wide bandgap restricts the response to visible light. The effects of the different surface termination and the doped atoms are investigated to manipulate the solar photocatalytic behavior of the surface. The results reveal that the band edges for the Ti/O-terminated (100) surface of SrTiO3 (SS-I) can straddle the redox potentials for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), but this is not true for the Sr/O-terminated one (SS-II). However, we successfully make the band edges of SS-II meet the HER and OER conditions by the doped Te and Po atoms (Te-SS-II and Po-SS-II), after trying the doped elements of the IIIA-VIA group. The solar-to-hydrogen efficiency are 14.50 %, 9.89 %, and 12.75 % for SS-I, Te-SS-II, and Po-SS-II, respectively. The Gibbs free energies are calculated for each HER and OER. The result of -0.34 eV for the HER on SS-I indicates that this reaction can spontaneously proceed. Therefore, these surfaces are promisingly used for photocatalytic water splitting. The present findings provide helpful guidance to manipulate the photocatalytic water splitting on the (100) surfaces of SrTiO3 by choosing the terminal atoms or doped atoms on the surface.

Structural impacts on the degradation behaviors of Ir-based electrocatalysts during water oxidation in acid

Large-scale hydrogen production by electrocatalytic water splitting still remains as a critical challenge due to the severe catalyst degradation during the oxygen evolution reaction (OER) in acidic media. In this study, we investigate the structural impacts on catalyst degradation behaviors using three iridium-based oxides, namely SrIrO3, Sr2IrO4, and Sr4IrO6 as model catalysts. These Ir oxides possess different connection configurations of [IrO6] octahedra units in their structure. Stable OER performance is observed on SrIrO3 and attributed to the edge-linked [IrO6] structure and rapid formation of a continuous IrOx layer on its surface, which functions not only as the “real” catalyst but also a shield preventing continuous cation leaching (with <1.0 at.% of Ir leaching). In comparison, both Sr2IrO4 and Sr4IrO6 catalysts demonstrate quick current fading with structure transformation to rutile IrO2 and formation of inconducive SrSO4 precipitates on surface, blocking the reactive sites. Nevertheless, over 60 at.% of Ir leaching is detected from the Sr4IrO6 catalyst due to its isolated [IrO6] structure configuration. Results of this work highlight the structural impacts on the catalyst stability in acidic OER conditions.

Spectroscopic Investigations of Complex Electronic Interactions by Elemental Doping and Material Compositing of Cobalt Oxide for Enhanced Oxygen Evolution Reaction Activity

AbstractDoping and compositing are two universal design strategies used to engineer the electronic state of a material and mitigate its disadvantages. These two strategies are extensively applied to design efficient electrocatalysts for water splitting. Using cobalt oxide (CoO) as a model catalyst, it is proven that the oxygen evolution reaction (OER) performance can be progressively improved, first by Fe‐doping to form Fe‐CoO solid solution, and further by the addition of CeO2 to produce a Fe‐CoO/CeO2 composite. X‐ray absorption spectroscopy (XAS) reveals that distinct electronic interactions are induced by the processes of doping and compositing. Fe‐doping of CoO can break down the structural symmetry, changing the electronic structure of both Co and O species at the surface and decreasing the flat‐band potential (Vfb). In comparison, subsequent compositing of Fe‐CoO with CeO2 induces negligible electronic changes in the Fe‐CoO (as seen in ex situ characterizations), but significantly modifies the oxidative transformations of both Co and Fe under OER conditions. The spectroscopic investigations reveal that Fe‐doping and CeO2 compositing play different roles in modifying the electronic properties of CoO in its pristine state and during OER catalysis, in return, providing useful guidance for the design of more efficient electrocatalysts using these two strategies.

Retaining the self-released chalcogenate at reconstructed cobalt sites by self-transformed carbonate regulation for boosted oxygen evolution

The in-situ generated oxyanions at electrochemically reconstructed catalysts from metal-based non-oxide compounds have been proven to significantly accelerate oxygen evolution reaction (OER) kinetics. However, it remains a challenge to retain these self-released oxyanions at reconstructed catalysts, hindering its utilization as a tool to develop efficient OER catalysts. Here, we demonstrate a versatile self-transformed carbonate regulation strategy to efficiently retain the self-released chalcogenate at Co oxyhydroxides reconstructed from carbon-incorporated Co selenides under OER conditions. These self-transformed CO32− can induce electron accumulation and narrow d bond at Co sites to facilitate the Co 3d–O 2p orbital hybridization between Co sites and SeOx2− for enhanced SeOx2− retention, which can accelerate the rate-limiting step for *OOH formation during OER. Relative to CoOOH-SeOx2− with limited SeOx2− residues, CoOOH-CO32−/SeOx2− with elevated SeOx2− retention by CO32− regulation exhibited a 5.6-fold increase in current density and a remarkable lower Tafel slope towards OER. This strategy paves a rational avenue to design efficient catalysts for electrooxidation reactions through finely regulating self-released oxyanions at reconstructed structures.

Structural and Electronic Factors behind the Electrochemical Stability of 3D-Metal Tungstates under Oxygen Evolution Reaction Conditions.

Transition metal tungstates (TMTs) possess a wolframite-like lattice structure and preferably form via an electrostatic interaction between a divalent transition metal cation (MII) and an oxyanion of tungsten ([WO4]2-). A unit cell of a TMT is primarily composed of two repeating units, [MO6]oh and [WO6]oh, which are held together via several M-μ2-O-W bridging links. The bond character (ionic or covalent) of this bridging unit determines the stability of the lattice and influences the electronic structure of the bulk TMT materials. Recently, TMTs have been successfully employed as an electrode material for various applications, including electrochemical water splitting. Despite the wide electrocatalytic applications of TMTs, the study of the structure-activity correlation and electronic factors responsible for in situ structural evolution to electroactive species during electrochemical reactions is still in its infancy. Herein, a series of TMTs, MIIWVIO4 (M = Mn/Fe/Co/Ni), have been prepared and employed as electrocatalysts to study the oxygen evolution reaction (OER) under alkaline conditions and to scrutinize the role of transition metals in controlling the energetics of the formation of electroactive species. Since the [WO6]oh unit is common in the TMTs considered, the variation of the central atom of the corresponding [MO6]oh unit plays an intriguing role in controlling the electronic structure and stability of the lattice under anodic potential. Under the OER conditions, a potential-dependent structural transformation of MWO4 is noticed, where MnWO4 appears to be the most labile, whereas NiWO4 is stable up to a high anodic potential of ∼1.68 V (vs RHE). Potential-dependent hydrolytic [WO4]2- dissolution to form MOx active species, traced by in situ Raman and various spectro-/microscopic analyses, can directly be related to the electronic factors of the lattice, viz., crystal field splitting energy (CFSE) of MII in [MO6]oh, formation enthalpy (ΔHf), decomposition enthalpy (ΔHd), and Madelung factor associated with the MWO4 ionic lattice. Additionally, the magnitude of the Löwdin and Bader charges on M of the M-μ2-O-W bond is directly related to the degree of ionicity or covalency in the MWO4 lattice, which indirectly influences the electronic structure and activity. The experimental results substantiated by the computational study explain the electrochemical activity of the TMTs with the help of various structural and electronic factors and bonding interactions in the lattice, which has never been realized. Therefore, the study presented here can be taken as a general guideline to correlate the reactivity to the structure of the inorganic materials.

Iron Triad-Based Bimetallic M–N–C Nanomaterials as Highly Active Bifunctional Oxygen Electrocatalysts

Iron Triad-Based Bimetallic M–N–C Nanomaterials as Highly Active Bifunctional Oxygen Electrocatalysts

Towards improved online dissolution evaluation of Pt-alloy PEMFC electrocatalysts via electrochemical flow cell - ICP-MS setup upgrades

Electrochemical flow cell coupled with an inductively coupled plasma mass spectrometer (EFC-ICP-MS) is a powerful electroanalytical technique to monitor in-situ dissolution of metallic electrocatalysts and to understand mechanism of degradation under operating conditions. Its utilisation has witnessed a notable increase in the electrocatalyst field in the last decade where it has been extensively used to study the stability of platinum group metals (PGMs) under oxygen reduction and oxygen evolution reaction conditions. Online ICP-MS has allowed the scientific and industrial community to optimise the activity and stability of PGMs thanks to a better understanding of the complex metal corrosion processes. Among the different setups, the electrochemical flow cell design is the most common as it is based on a commercially available design. Nonetheless, besides different materials and different electrochemical protocols, the impact of the geometry and various parameters of the setup on the recorded dissolution signal has not been studied until now. Such parameters can influence the results obtained with an EFC-ICP-MS and thus the interpretation of the dissolution mechanism and/or stability assessment. Hereby, we demonstrate that the length of the tubing between the outlet of the cell and the inlet of the ICP-MS impacts the resolution of the PtCo catalyst dissolution peaks. This, in turn, facilitates studies where the detection of extremely low concentrations is necessary, such as under a very narrow potential window. Similarly, a reduced internal volume of the cell restricts Pt redeposition, contributing to a more precise evaluation of stability. These claims were supported by dynamic continuum mechanics modelling of the ion concentration in a model EFC. Finally, we provide guidelines and advice to properly measure dissolution with an electrochemical cell coupled with ICP-MS.

Mesoporous Single Atom-Cluster Fe-N/C Oxygen Evolution Electrocatalysts Synthesized with Bottlebrush Block Copolymer-Templated Rapid Thermal Annealing.

Current electrocatalysts for oxygen evolution reaction (OER) are either expensive (such as IrO2, RuO2) or/and exhibit high overpotential as well as sluggish kinetics. This article reports mesoporous earth-abundant iron (Fe)-nitrogen (N) doped carbon electrocatalysts with iron clusters and closely surrounding Fe-N4 active sites. Unique to this work is that the mechanically stable mesoporous carbon-matrix structure (79 nm in pore size) with well-dispersed nitrogen-coordinated Fe single atom-cluster is synthesized via rapid thermal annealing (RTA) within only minutes using a self-assembled bottlebrush block copolymer (BBCP) melamine-formaldehyde resin composite template. The resulting porous structure and domain size can be tuned with the degree of polymerization of the BBCP backbone, which increases the electrochemically active surface area and improves electron transfer and mass transport for an effective OER process. The optimized electrocatalyst shows a required potential of 1.48 V (versus RHE) to obtain the current density of 10 mA/cm2 in 1 M KOH aqueous electrolyte and a small Tafel slope of 55 mV/decade at a given overpotential of 250 mV, which is significantly lower than recently reported earth-abundant electrocatalysts. Importantly, the Fe single-atom nitrogen coordination environment facilitates the surface reconstruction into a highly active oxyhydroxide under OER conditions, as revealed by X-ray photoelectron spectroscopy and in situ Raman spectroscopy, while the atomic clusters boost the single atoms reactive sites to prevent demetalation during the OER process. Density functional theory (DFT) calculations support that the iron nitrogen environment and reconstructed oxyhydroxides are electrocatalytically active sites as the kinetics barrier is largely reduced. This work has opened a new avenue for simple, rapid synthesis of inexpensive, earth-abundant, tailorable, mechanically stable, mesoporous carbon-coordinated single-atom electrocatalysts that can be used for renewable energy production.

Intermetallic Cobalt Indium Nanoparticles as Oxygen Evolution Reaction Precatalyst: A Non-Leaching p-Block Element.

Merely all transition-metal-based materials reconstruct into similar oxyhydroxides during the electrocatalytic oxygen evolution reaction (OER), severely limiting the options for a tailored OER catalyst design. In such reconstructions, initial constituent p-block elements take a sacrificial role and leach into the electrolyte as oxyanions, thereby losing the ability to tune the catalyst's properties systematically. From a thermodynamic point of view, indium is expected to behave differently and should remain in the solid phase under alkaline OER conditions. However, the structural behavior of transition metal indium phases during the OER remains unexplored. Herein, are synthesized intermetallic cobalt indium (CoIn3) nanoparticles and revealed by in situ X-ray absorption spectroscopy and scanning transmission microscopy that they undergo phase segregation to cobalt oxyhydroxide and indium hydroxide. The obtained cobalt oxyhydroxide outperforms a metallic-cobalt-derived one due to more accessible active sites. The observed phase segregation shows that indium behaves distinctively differently from most p-block elements and remains at the electrode surface, where it can form lasting interfaces with the active metal oxo phases.

Atomistic Modeling of Spinel Oxide Particle Shapes and Reshaping under OER Conditions

The surface configurations of the low-index facets of a set of spinel oxides are investigated using DFT+U calculations to derive surface energies and predict equilibrium nanoparticle shapes via the Wulff construction. Two very different conditions are investigated, corresponding to application either in heterogeneous catalysis or in electrocatalysis. First, the bare stoichiometric surfaces of NiFe2O4, CoFe2O4, NiCo2O4, and ZnCo2O4 spinels are studied to model their use as high-temperature oxidation catalysts. Second, focusing attention on the electrochemical oxygen evolution reaction (OER) and on the CoFe2O4 inverse spinel as the most promising OER catalyst, we generate surface configurations by adsorbing OER intermediates and, in an innovative study, we recalculate surface energies taking into account adsorption and environmental conditions, i.e., applied electrode potential and O2 pressure. We predict that under OER operating conditions, (111) facets are dominant in CoFe2O4 nanoparticle shapes, in fair agreement with microscopy measurements. Importantly, in the OER case, we predict a strong dependence of nanoparticle shape upon O2 pressure. Increasing O2 pressure increases the size of the higher-index (111) and (110) facets at the expense of the (001) more catalytically active facet, whereas the opposite occurs at low O2 pressure. These predictions should be experimentally verifiable and help define the optimal OER operative conditions.

Low-coordinated surface nickel oxide as electrocatalyst for efficient water oxidation

Ni-based compounds represent promising candidates as high-performance electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. Here, a new Ni oxide electrocatalyst developed via a simple electrodeposition method is reported, exhibiting enhanced catalytic activity for OER. Structural and activity analysis of the fresh and post-reaction samples reveals that the Ni2+ center has low coordination with pyramidal symmetry (NiO5). The bulk metallic Ni readily undergoes oxidation under OER conditions to generate more low-coordinated Ni2+ and high-valence state Ni (Ni3+) species, thereby facilitating the OER reaction. This study provides new insight into the active structure of Ni-based oxide electrocatalysts and offers a simple pathway for the design and development of cost-effective and high-performance electrocatalysts for applications in OER.

Separating the Effects of Band Bending and Covalency in Hybrid Perovskite Oxide Electrocatalyst Bilayers for Water Electrolysis

Testing single crystalline epitaxial thin films as model systems for metal oxide electrocatalysts in the oxygen evolution reaction (OER) enables differentiating the OER descriptors such as crystal facet orientation, surface chemical composition, electronic structure and band bending at the interface to the electrolyte [1,2,3]. We designed single crystalline perovskite oxide bilayer structures to systematically tune the surface electronic structure and the band bending at the electrode/electrolyte interface to understand their role in the OER.The Co−O covalency in perovskite oxide cobaltites such as La1 − x SrxCoO3 is believed to impact the electrocatalytic activity during the OER. Additionally, space charge layers through band bending at the interface to the electrolyte may affect the electron transfer into the electrode, complicating the analysis and identification of true OER activity descriptors. Here, we separate the influence of covalency and band bending in hybrid epitaxial bilayer structures of highly OER-active La0.6Sr0.4CoO3 and undoped and less-active LaCoO3. Ultrathin LaCoO3 capping layers of 2−8 unit cells on La0.6Sr0.4CoO3 show intermediate OER activity between La0.6Sr0.4CoO3 and LaCoO3 evidently caused by the increased surface Co−O covalency compared to single LaCoO3 as detected by X-ray photoelectron spectroscopy. A Mott−Schottky analysis revealed low flat band potentials for different LaCoO3 capping layer thicknesses, indicating that no limiting extended space charge layer exists under OER conditions as all catalyst bilayer films exhibited hole accumulation at the surface [1].The combined X-ray photoelectron spectroscopy and Mott−Schottky analysis of atomically defined bilayer structures thus enables us to differentiate between the influence of the covalency and intrinsic space charge layers, which are indistinguishable in a single physical or electrochemical characterization. Our results emphasize the prominent role of transition metal oxygen covalency in perovskite electrocatalysts and introduce a bilayer approach to fine-tune the surface electronic structure [1].[1] L. Heymann, M. L. Weber, M. Wohlgemuth, M. Risch, R. Dittmann, C. Baeumer, F. Gunkel (2022) Separating the Effects of Band Bending and Covalency in Hybrid Perovskite Oxide Electrocatalyst Bilayers for Water Electrolysis, ACS Appl. Mater. Interfaces[2] M. Wohlgemuth, M. L. Weber, L. Heymann, C. Baeumer, F. Gunkel (2022) Activity-Stability Relationships in Oxide Electrocatalysts for Water Electrolysis, Front. Chem.[3] M. L. Weber, G. Lole, A. Kormanyos, A. Schwiers, L. Heymann, F. D. Speck, T. Meyer, R. Dittmann, S. Cherevko, C. Jooss, C. Baeumer, F. Gunkel, (2022) Atomistic Insights into Activation and Degradation of La0.6Sr0.4CoO3-δ Electrocatalysts under Oxygen Evolution Conditions Figure 1

Self-Terminated Surface Reconstruction of Lanthanum Nickelates Promotes Alkaline Oxygen Evolution

Oxygen evolution reaction (OER) itself is expected to have a strong impact on the state of the surface of the electrocatalyst, yet the actual structure of the surface under operating conditions is rarely considered while formulating structure-activity correlations in electrocatalysis. In this study, changes in the surface structure of Ruddlesden-Popper-type lanthanum nickelate, La2NiO4+δ, and the perovskite LaNiO3 are probed and contrasted using a series of complementary surface sensitive techniques, including XPS, HRTEM and O K-edge XAS. We found noticeable surface changes to occur on La2NiO4+δ after exposure its exposure to the alkaline electrolyte that is accompanied by the emergence of a strong Nin+/n+1 redox feature and the coincides with a 45-fold enhancement of the OER activity (at η = 370 mV) in 0.1 M KOH, as compared to the pristine La2NiO4+δ phase. We observe that the in situ formation of an amorphous nickel (oxy)hydroxide layer on the surface increases the electrochemically-active surface area of La2NiO4+δ and imparts a high stability of the catalyst under OER conditions (the formation of the amorphous layer self-terminates at ca. 3 nm). In addition, the transition from octahedral Ni sites (O h ) to square-planar Ni sites (D 4h ) in the reconstructed surface was observed using O K-edge X-ray absorption spectroscopy. Further, we found no evidence for any surface transformations in the perovskite-based catalyst LaNiO3 that also did not demonstrate any improvement in its activity over cycling. This work highlights the importance of a detailed surface analysis of the catalysts under operation to build robust structure-activity correlations for the metal oxides under electrochemical reaction conditions. Figure 1

Towards Reliable Stability Measurements of OER Catalysts

Currently, significant efforts are taken to find the most active and stable electrochemical oxygen evolution reaction (OER) catalyst diverting from critical raw material. However, one also needs to consider new catalyst screening methods, especially with respect to stability investigations where rotating disk electrode (RDE) studies are not suitable.1 Recently, we introduced a gas diffusion electrode (GDE) setup as a new testing platform for OER catalysts.2 This methodology stems from fuel cell studies where carbon gas diffusion layer (GDL) is used as a transport layer to bring the reactant to the catalyst. Since carbon is not stable under the harsh OER conditions, water electrolyser uses titanium-based porous transport layers (PTLs). In the current work, we utilized the GDE setup to test the influence of the transport layer on the stability of a highly active Ir0.7Ru0.3Ox nanoparticle catalyst immobilized on homemade antimony-doped tin oxide (ATO) support. The test was conducted potentiostatically (@ 1.6 V vs RHE) for 2 h at 60 °C. The stability of the catalyst was then compared when deposited on GDL vs PTL. Rapid decline of the GDL-deposited catalyst activity was observed, while the PTL-deposited catalyst demonstrates a rather stable behavior (Fig. 1). We attribute this fast activity drop to the carbon oxidation of the GDL. Moreover, the activity at 30 °C of the PTL-deposited catalyst was compared to literature data on RDE setup [1]. In the RDE setup, a breakdown is observed after only 30 min when applying a constant current density. In contrast, PTL-deposited catalyst exhibits no activity loss during 2 h under similar conditions.[1] H. A. El-Sayed. Journal of The Electrochemical Society, 166 (8), F458-F464 (2019)[2] J. Schröder. JACS Au, 1, 247-251 (2021) Figure 1 . Potentiostatic stability transients at 1.6 V vs RHE of Ir0.7Ru0.3Ox/ATO deposited on C-based GDL (green full) and on Ti-based PTL at 60 °C (black full) and 30 °C (blue dashed). Figure 1

Transforming materials discovery for artificial photosynthesis: High-throughput screening of earth-abundant semiconductors

We present a highly efficient workflow for designing semiconductor structures with specific physical properties, which can be utilized for a range of applications, including photocatalytic water splitting. Our algorithm generates candidate structures composed of earth-abundant elements that exhibit optimal light-trapping, high efficiency in H2 and/or O2 production, and resistance to reduction and oxidation in aqueous media. To achieve this, we use an ionic translation model trained on the Inorganic Crystal Structure Database to predict over 30 000 undiscovered semiconductor compositions. These predictions are then screened for redox stability under hydrogen evolution reaction or oxygen evolution reaction conditions before generating thermodynamically stable crystal structures and calculating accurate bandgap values for the compounds. Our approach results in the identification of dozens of promising semiconductor candidates with ideal properties for artificial photosynthesis, offering significant advancement toward the conversion of sunlight into chemical fuels.