Evaluating transition metal molybdates as catalysts in hydrogen production

Hydrogen is a potential clean energy source that could replace fossil fuels in the future. However, producing it without emitting carbon dioxide requires large amounts of electricity, which makes clean hydrogen too expensive for large-scale use. Making hydrogen more efficiently requires optimizing the oxygen evolution reaction (OER) that produces hydrogen from water.

Hao et al. investigated cobalt-nickel molybdate (CoNiMoO₄) nanowires to determine the transition these metals undergo during OER.

One of the most common ways to improve the efficiency of the OER is to use a pre-catalyst, a substance that is converted into a catalyst during a chemical cycle, and transition metals like molybdates are promising candidates. In the OER, molybdate electrodes undergo a dynamic conversion process into highly active hydroxyl oxides, greatly increasing the reaction speed. However, this transformation process is still not well understood.

“Our research aims to elucidate the dynamic structural evolution of transition metal-based catalysts to establish robust structure-activity relationships, thereby advancing the fundamental theory of electrocatalysis and providing guidance for the development of efficient OER catalysts,” said author Bo Wei.

Using Raman spectroscopy and ultraviolet-visible spectroscopy, the authors observed CoNiMoO₄ undergoing remodeling during the OER, reacting to form hydroxide followed by oxyhydroxide (CoNiOOH) at high potentials. They employed density functional theory to show that the increased OER activity was due to the d-band center modulation in CoNiOOH enhancing the adsorption capacity for oxygen intermediates.

“In future studies, we aim to explore the effects of doping other metal elements or constructing heterojunctions on the catalytic activity,” said Wei. “In addition, we intend to extend the application of CoNiMoO₄ catalysts to other electrochemical reactions, such as organic oxidation.”

Source: “Operando spectroscopic monitoring the dynamic transformation of CoNiMoO₄ precatalyst towards efficient oxygen evolution,” by Hongru Hao, Jiahui Wang, Jian Zhou, Zhe Wang, Shuo Shen, LingLing Xu, Zhe Lv, and Bo Wei, Applied Physics Letters (2025). The article can be accessed at https://doi.org/10.1063/5.0267368 .