Fe-Doped Ni-Based Catalysts Surpass Ir-Baselines for Oxygen Evolution Due to Optimal Charge-Transfer Characteristics

• Published in: ACS catalysis 2024-12, Vol.14 (23), p.17347-17359
• Main Authors: Ha, Mai-Anh, Alia, Shaun M., Norman, Andrew G., Miller, Elisa M.
• Format: Article
• Language: English
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.4c04489

Ni-based catalysts with Co or Fe can potentially replace precious Ir-based catalysts for the rate-limiting oxygen evolution reaction (OER) in anion-exchange membrane (AEM) electrolyzers. In this study, density functional theory (DFT) calculations provide atomic- and electronic-level resolution on how the inclusion of Co or Fe can overcome the inactivity of NiO catalysts and even enable them to surpass IrO2 in activating key steps to the OER. Namely, NiO resists binding the key OH* intermediate and presents a high energetic barrier to forming the O*. Co- and Fe-substitution of Ni active sites allows for the stronger binding of OH* and preferentially activates O*/O2* formation, with Fe-substitution increasing the OER activity substantially as compared to Co-substitution. Whereas IrO2 requires an activation energy of 0.34–0.49 eV to form O2, this step is spontaneous on Fesub-NiO. Electrodeposition of polycrystalline electrodes and synthesized nanoparticles exploit the Co or Fe presence, with Fe particularly exhibiting greater activity: Tafel slopes indicate a significant change in the mechanism as compared to pure NiO, validating the theoretical predictions of OER activation at different steps. High-performing synthesized nanoparticles of 25% Fe–Ni exhibited a 4.6 times improvement over IrO2 and a 34% improvement over RuO2, showcasing that non-platinum group metal catalysts can outperform platinum group metals. High-resolution transmission electron microscopy further highlights the advantages of Fe–Ni oxide synthesized nanoparticles over commercial catalysts: small, randomly oriented nanoparticles expose greater edge sites than large nanoparticles typical of commercially available materials.