The oxygen evolution reaction (OER) is a cornerstone of various energy storage applications, including metal-air batteries, water electrolyzers, and CO2 reduction. While noble metal catalysts like iridium and ruthenium exhibit excellent OER performance, their scarcity and high cost drive the search for cost-effective alternatives. Nickel, cobalt, and iron-based electrodes show promise but fall short of industrial requirements in terms of long-term stability and high current density operation (>1000 h at >1000 mA cm⁻²). NiFe-LDHs, with their 2D lamellar structure and tunable electronic properties, are attractive candidates, but their performance is hampered by scaling relationships between the binding energies of reaction intermediates and the inherent instability caused by metal leaching during prolonged operation. Strategies such as morphology control, vacancy engineering, and doping have improved activity, but resolving dynamic limitations and metal dissolution remains a significant challenge. This work draws inspiration from the Mn4Ca oxo cluster in Photosystem II and the role of carboxylate ligands in stabilizing metal clusters in enzymes, suggesting that introducing specific ligands could enhance both the activity and stability of heterogeneous catalysts.

Extensive research focuses on improving the OER activity and stability of NiFe-LDHs. Previous studies have highlighted the issue of rapid degradation due to metal dissolution under alkaline OER conditions. While methods to enhance activity exist, inhibiting metal dissolution at the atomic level, especially under industrial conditions, remains a significant hurdle. Mimicking enzymatic systems with specific binding through carboxylate ligands offers a potential solution. Carboxylate ligands from amino acid residues are known to stabilize metal clusters in homogeneous systems, promoting proton transfer via concerted proton-electron transfer (CPET) processes. This approach has been successful in homogeneous systems but its application in heterogeneous catalysts and the synergy between carboxylate anchoring and multi-metal active sites require further investigation.

This study introduces a sub-size NiFe-LDH nanosheet catalyst modified with trimesic acid (SU-NiFe-LDH(TA)) prepared via electrochemical deposition on carbon paper. Two versions were synthesized: NiFe-LDH(TA)@cp using FeSO₄·7H₂O and SU-NiFe-LDH(TA)@cp using Fe(NO₃)₃·9H₂O. The electrochemical deposition process, involving Ni(NO₃)₂·6H₂O, FeSO₄·7H₂O or Fe(NO₃)₃·9H₂O, trimesic acid, and a carbon paper substrate, allowed for the incorporation of both coordinated and uncoordinated carboxylate ligands. The resulting catalysts were characterized using XRD, HR-TEM, SEM, SAED, FTIR, Raman, and XPS to analyze their phase composition, morphology, and electronic structure. Electrochemical measurements, including LSV, Tafel plots, EIS, and chronoamperometry, were conducted in 1 M KOH and 6 M KOH at 60 °C to evaluate OER activity and stability. In situ Raman and FTIR spectroscopy were used to monitor the dynamic evolution of the carboxylate ligands during the OER. DFT calculations were performed to investigate the electronic structure and reaction mechanisms.

The SU-NiFe-LDH(TA)@cp catalyst exhibited significantly enhanced OER performance compared to NiFe-LDH@cp and NiFe-LDH(TA)@cp. It demonstrated a lower overpotential (248 mV at 100 mA cm⁻²) and a smaller Tafel slope (31.1 mV dec⁻¹). The catalyst also showed exceptional long-term stability, maintaining its activity at 1500 mA cm⁻² for over 1300 h in 1 M KOH and at 1000 mA cm⁻² for over 800 h under industrial conditions (60 °C, 6 M KOH). Contact angle measurements revealed the superhydrophilic and superaerophobic nature of SU-NiFe-LDH(TA)@cp, facilitating efficient O2 bubble release. In situ Raman and FTIR spectroscopy provided evidence for both static coordination of carboxylates to metal centers via C-O-Fe bonds, stabilizing the structure, and dynamic evolution of uncoordinated carboxylates, which act as proton ferries to accelerate the OER kinetics. DFT calculations confirmed that the ligands stabilize the electronic structure, reduce the energy barriers for the rate-determining steps, and facilitate proton transfer through the lengthening of O-H bonds in reaction intermediates. ICP-MS analysis demonstrated a significant reduction in metal ion dissolution for the trimesic acid-modified catalysts compared to the unmodified NiFe-LDH@cp.

The findings demonstrate the successful implementation of a bioinspired strategy to enhance OER electrocatalyst performance. The combination of static and dynamic compatibility of the trimesic acid ligands leads to a synergistic effect on both stability and activity. The static coordination through C-O-Fe bonds effectively inhibits metal dissolution, while the dynamic proton transfer facilitated by uncoordinated carboxylates accelerates the reaction kinetics. The superior performance under industrial conditions highlights the potential for practical applications. The superhydrophilic and superaerophobic surface properties further contribute to the improved performance by promoting efficient gas bubble detachment and mass transport. These results provide insights into the design of high-performance and stable OER electrocatalysts and offer a promising approach for overcoming limitations in current water electrolysis technologies.

This study successfully demonstrates a bioinspired strategy for designing highly active and durable OER electrocatalysts. The use of trimesic acid ligands introduces both static and dynamic compatibility, resulting in superior OER performance and long-term stability under challenging conditions. The findings provide valuable insights into the design principles of advanced OER electrocatalysts and pave the way for practical applications in high-current water electrolysis. Future research could explore other bioinspired ligands and different LDH compositions to further optimize catalytic performance and explore the scalability and industrial implementation of this technology.

While the study demonstrates significant improvements in OER performance and stability, further investigation is needed to fully understand the long-term stability under even more extreme industrial conditions. The scalability of the electrochemical deposition method should be explored for larger-scale production. The specific influence of different types of carbon substrates on the overall performance could be explored in greater depth.