Origin of the superior oxygen reduction activity of zirconium nitride in alkaline media

Closed-Loop Framework for Discovering Stable and Low-Cost Bifunctional Metal Oxide Catalysts for Efficient Electrocatalytic Water Splitting in Acid

Electrocatalytic water splitting, comprising the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), provides a sustainable route for hydrogen production. While low-cost metal oxides (MOs) are appealing as alternatives to noble metal electrocatalysts, their application in acidic media remains challenging. However, the dynamic nature of some MO surface structures under electrochemical conditions offers an opportunity for rational catalyst design to achieve bifunctionality in acidic OER and HER. Here, we present a closed-loop framework that integrates potential catalyst exploration (front-end), synthesis and electrochemical tests (mid-end), and advanced characterizations (back-end). This framework combines crucial steps in electrocatalyst exploration, including data mining, surface state analysis, microkinetic modeling, and proof-of-concept experiments to identify stable and cost-effective MO catalysts for acidic water splitting. Using this approach, RbSbWO6 is identified as a promising bifunctional catalyst for the first time, with experimental validation demonstrating its exceptional stability and performance under acidic OER and HER. Notably, RbSbWO6 outperforms many other reported non-noble stoichiometric MO catalysts that have not undergone major modifications for acidic water splitting. These findings, derived from our Digital Catalysis Platform (DigCat), establish RbSbWO6 as a highly effective non-noble stoichiometric bifunctional MO catalyst and underscore the power of our closed-loop workflow for accelerating catalyst discovery. This framework begins with the DigCat platform, concludes with experimental validation, and feeds into the platform, demonstrating its potential for designing electrocatalysts in other systems such as metal nitrides or carbides. This study demonstrates the importance and high efficiency of data-driven approaches as a new scientific discovery paradigm.

A mechanism-guided descriptor for the hydrogen evolution reaction in 2D ordered double transition-metal carbide MXenes

Selecting effective catalysts for the hydrogen evolution reaction (HER) among MXenes remains a complex challenge. While machine learning (ML) paired with density functional theory (DFT) can streamline this search, issues with training data quality, model accuracy, and descriptor selection limit its effectiveness. These hurdles often arise from an incomplete understanding of the catalytic mechanisms. Here, we introduce a mechanism-guided descriptor (δ) for the HER, designed to enhance catalyst screening among ordered transition metal carbide MXenes. This descriptor integrates structural and energetic characteristics, derived from an in-depth analysis of orbital interactions and the relationship between Gibbs free energy of hydrogen adsorption (ΔG H) and structural features. The proposed model (ΔG H = -0.49δ - 2.18) not only clarifies structure-activity links but also supports efficient, resource-effective identification of promising catalysts. Our approach offers a new framework for developing descriptors and advancing catalyst screening.

W-Mediated Electron Accumulation in Ru-O-W Motifs Enables Ultra-Stable Oxygen Evolution Reaction in Acid

The development of efficient and durable oxygen evolution reaction (OER) catalysts is crucial for advancing proton exchange membrane water electrolysis (PEMWE) technology, especially in the pursuit of non-iridium alternatives. Herein, we report a Zn, W co-doped Ru3Zn0.85W0.15Ox (RZW) ternary oxide catalyst that exhibits a low overpotential of 200 mV and remarkable stability for over 4000 hours at 10 mA cm-2 in 0.1 M HClO4. The incorporation of highly electronegative W facilitates the efficient capture of electrons released from the sacrificial Zn species during OER, and subsequently mediated to Ru sites. The observed enhancement in electron density within the stable Ru-O-W motifs substantially improves the anti-overoxidation properties of the Ru active sites. Our findings highlight the importance of strategic metal doping in modulating the electronic structure of OER catalysts during operation, thereby facilitating the development of practical and long-lasting water electrolysis technologies.

Well-Defined PtCo@Pt Core-Shell Nanodendrite Electrocatalyst for Highly Durable Oxygen Reduction Reaction

The rational design of efficient electrocatalysts with controllable structure and composition is crucial for enhancing the lifetime and cost-effectiveness of oxygen reduction reaction (ORR). PtCo nanocrystals have gained attention due to their exceptional activity, yet suffer from stability issues in acidic media. Herein, an active and highly stable electrocatalyst is developed, namely 3D Pt7Co3@Pt core-shell nanodendrites (NDs), which are formed through the self-assembly of small Pt nanoparticles (≈6 nm). This unique structure significantly improves the ORR with an enhanced mass activity (MA) of 0.54 A mgPt -1, surpassing that of the commercial Pt/C (com-Pt/C) catalyst by three fold (0.17 A mgPt -1). The well-organized dendritic morphology, along with the Pt-rich shell, contributes significantly to the observed high catalytic activity and superior stability for acidic ORR, which exhibit a loss of 2.1% in MA and, impressively, an increase of 12.0% in specific activity (SA) after an accelerated durability test (ADT) of 40,000 potential-scanning cycles. This work offers insights for improving the design of highly stable Pt-based electrocatalysts for acidic ORR.

Importing Atomic Rare-Earth Sites to Activate Lattice Oxygen of Spinel Oxides for Electrocatalytic Oxygen Evolution

Spinel oxides have emerged as highly active catalysts for the oxygen evolution reaction (OER). Owing to covalency competition, the OER process on spinel oxides often follows an arduous adsorbate evolution mechanism (AEM) pathway. Herein, we propose a novel rare-earth sites substitution strategy to tune the lattice oxygen redox of spinel oxides and bypass the AEM scaling relationship limitation. Taking NiCo2O4 as a model, the incorporation of Ce into the octahedral site induces the formation of Ce-O-M (M=Ni, Co) bridge, which triggers charge redistribution within NiCo2O4. The developed Ce-NiCo2O4 exhibits remarkable OER activity with a low overpotential, satisfactory electrochemical stability, and good practicability in anion-exchange membrane water electrolyzer. Theoretical analyses reveal that OER on Ce-NiCo2O4 surface follows a more favorable lattice oxygen mechanism (LOM) pathway and non-concerted proton-electron transfers compared to pure NiCo2O4, as also verified by pH-dependent behavior and in situ Raman analysis. The 18O-labeled electrochemical mass spectrometry provides direct evidence that the oxygen released during the OER originates from the lattice oxygen of Ce-NiCo2O4. We discover that electron delocalization of Ce 4f states triggers charge redistribution in NiCo2O4 through the Ce-O-M bridge, favoring antibonding state occupation of Ni-O bonding in [Ce-O-Ni] unit site, thereby activating lattice oxygen redox of NiCo2O4 in OER. This work provides a new perspective for designing highly active spinel oxides for OER and offers significant insights into the rare-earth-enhanced LOM mechanism.

Surface coverage and reconstruction analyses bridge the correlation between structure and activity for electrocatalysis

Electrocatalysis is key to realizing a sustainable future for our society. However, the complex interface between electrocatalysts and electrolytes presents an ongoing challenge in electrocatalysis, hindering the accurate identification of effective/authentic structure-activity relationships and determination of favourable reaction mechanisms. Surface coverage and reconstruction analyses of electrocatalysts are important to address each conjecture and/or conflicting viewpoint on surface-active phases and their corresponding electrocatalytic origin, i.e., so-called structure-activity relationships. In this review, we emphasize the importance of surface states in electrocatalysis experimentally and theoretically, providing guidelines for research practices in discovering promising electrocatalysts. Then, we summarize some recent progress of how surface states determine the adsorption strengths and reaction mechanisms of occurring electrocatalytic reactions, exemplified in the electrochemical oxygen evolution reaction, oxygen reduction reaction, nitrogen reduction reaction, CO2 reduction reaction, CO2 and N2 co-reductions, and hydrogen evolution reaction. Finally, the review proposes deep insights into the in situ study of surface states, their efficient building and the application of surface Pourbaix diagrams. This review will accelerate the development of electrocatalysts and electrocatalysis theory by arousing broad consensus on the significance of surface states.

Ru-catalyzed activation of free phenols in a one-step Suzuki-Miyaura cross-coupling under mechanochemical conditions

Activation of phenols by a Ru-catalyst allows for the resulting η5-phenoxo complex to selectively react with a variety of nucleophiles under mechanochemical conditions. Conversion of phenolic hydroxy groups without derivatization is important for late-stage modifications of pharmaceuticals and in the context of lignin-material processing. We present a one-step, Ru-catalyzed cross-coupling of phenols with boronic acids, aryl trialkoxysilanes and potassium benzoyltrifluoroborates under mechano-chemical conditions. The protocol accepts a wide scope of starting materials and allows for gram-scale synthesis in excellent yields. The developed approach constitutes a very interesting and waste-limiting alternative to the known methods.

Reversible Hydrogen Electrode (RHE) Scale Dependent Surface Pourbaix Diagram at Different pH

In the analysis of electrocatalysis mechanisms and the design of catalysts, the effect of electrochemistry-induced surface coverage is a critical consideration that should not be overlooked. The surface Pourbaix diagram emerges as a fundamental tool in this context, providing essential insights into the surface coverage of adsorbates generated via electrochemical potential-driven water activation. A classic surface Pourbaix diagram considers the pH effects by correcting the free energy of H+ ions by the concentration-dependent term: -kBT ln(10) × pH, which is independent of the reversible hydrogen electrode (RHE) scale. However, this is sometimes inconsistent with the experimentally observed potential-dependent surface coverage at an RHE scale, especially under high-pH conditions. Here, we derived the pH-dependent surface Pourbaix diagram at an RHE scale by considering the energetics computed by density functional theory with the Bayesian Error Estimation Functional with van der Waals corrections (BEEF-vdW), the electric field effects, the derived adsorption-induced dipole moment and polarizability, and the potential of zero-charge. Using Pt(111) as the typical example, we found that the surface coverage predicted by the proposed RHE-dependent surface Pourbaix diagram can significantly minimize the discrepancy between theory and experimental observations, especially under neutral-alkaline, moderate-potential conditions. This work provides a new methodology and establishes guidelines for the precise analysis of the surface coverage prior to the evaluation of the activity of an electrocatalyst.

Deciphering Structure-Activity Relationship Towards CO2 Electroreduction over SnO2 by A Standard Research Paradigm

Authentic surface structures under reaction conditions determine the activity and selectivity of electrocatalysts, therefore, the knowledge of the structure-activity relationship can facilitate the design of efficient catalyst structures for specific reactivity requirements. However, understanding the relationship between a more realistic active surface and its performance is challenging due to the complicated interface microenvironment in electrocatalysis. Herein, we proposed a standard research paradigm to effectively decipher the structure-activity relationship in electrocatalysis, which is exemplified in the CO2 electroreduction over SnO2 . The proposed practice has aided in discovering authentic/resting surface states (Sn layer) of SnO2 accountable for the electrochemical CO2 reduction reaction (CO2 RR) performance under electrocatalytic conditions, which then is corroborated in the subsequent CO2 RR experiments over SnO2 with different morphologies (nanorods, nanoparticles, and nanosheets) in combination with in situ characterizations. This proposed methodology is further extended to the SnO electrocatalysts, providing helpful insights into catalytic structures. It is believed that our proposed standard research paradigm is also applicable to other electrocatalytic systems, in the meantime, decreases the discrepancy between theory and experiments, and accelerates the design of catalyst structures that achieve sustainable performance for energy conversion.

Identifying Stable Electrocatalysts Initialized by Data Mining: Sb2 WO6 for Oxygen Reduction

Data mining from computational materials database has become a popular strategy to identify unexplored catalysts. Herein, the opportunities and challenges of this strategy are analyzed by investigating a discrepancy between data mining and experiments in identifying low-cost metal oxide (MO) electrocatalysts. Based on a search engine capable of identifying stable MOs at the pH and potentials of interest, a series of MO electrocatalysts is identified as potential candidates for various reactions. Sb2 WO6 attracted the attention among the identified stable MOs in acid. Based on the aqueous stability diagram, Sb2 WO6 is stable under oxygen reduction reaction (ORR) in acidic media but rather unstable under high-pH ORR conditions. However, this contradicts to the subsequent experimental observation in alkaline ORR conditions. Based on the post-catalysis characterizations, surface state analysis, and an advanced pH-field coupled microkinetic modeling, it is found that the Sb2 WO6 surface will undergo electrochemical passivation under ORR potentials and form a stable and 4e-ORR active surface. The results presented here suggest that though data mining is promising for exploring electrocatalysts, a refined strategy needs to be further developed by considering the electrochemistry-induced surface stability and activity.

Importing Antibonding-Orbital Occupancy through Pd-O-Gd Bridge Promotes Electrocatalytic Oxygen Reduction

The active-site density, intrinsic activity, and durability of Pd-based materials for oxygen reduction reaction (ORR) are critical to their application in industrial energy devices. This work constructs a series of carbon-based rare-earth (RE) oxides (Gd2 O3 , Sm2 O3 , Eu2 O3 , and CeO2 ) by using RE metal-organic frameworks to tune the ORR performance of the Pd sites through the Pd-REx Oy interface interaction. Taking Pd-Gd2 O3 /C as a representative, it is identified that the strong coupling between Pd and Gd2 O3 induces the formation of the Pd-O-Gd bridge, which triggers charge redistribution of Pd and Gd2 O3 . The screened Pd-Gd2 O3 /C exhibits impressive ORR performance with high onset potential (0.986 VRHE ), half-wave potential (0.877 VRHE ), and excellent stability. Similar ORR results are also found for Pd-Sm2 O3 /C, Pd-Eu2 O3 /C, and Pd-CeO2 /C catalysts. Theoretical analyses reveal that the coupling between Pd and Gd2 O3 promotes electron transfer through the Pd-O-Gd bridge, which induces the antibonding-orbital occupancy of Pd-*OH for the optimization of *OH adsorption in the rate-determining step of ORR. The pH-dependent microkinetic modeling shows that Pd-Gd2 O3 is close to the theoretical optimal activity for ORR, outperforming Pt under the same conditions. By its ascendancy in ORR, the Pd-Gd2 O3 /C exhibits superior performance in Zn-air battery as an air cathode, implying its excellent practicability.