Novel monoclinic ABO₄ oxide with single-crystal structure as next generation electrocatalyst for oxygen evolution reaction

Designing highly active and stable electrocatalysts to efficiently catalyze oxygen evolution reaction (OER) plays a crucial role in hydrogen production from water splitting. Here, we develop a novel monoclinic ABO₄-type metal oxide as versatile candidate for high performance OER catalysis. It has a flexible multi-metal composition and tunable structure which can rationally optimize the OER catalytic activities of ABO₄-type oxide. Remarkably, the obtained single-crystal Fe_0.4Co_0.6W_0.4Mo_0.6O₄ shows an excellent OER catalytic activity with an overpotential of 276.4 mV at 10 mA cm⁻², as well as an ultra-low Tafel slope of 30.9 mV decade⁻¹, which outperforms that of the state-of-the-art RuO₂ electrocatalyst. Mechanism analysis by density functional theory calculations confirms that the octahedral A sites with low valence state can serve as the active sites in ABO₄-type oxide for OER. In addition, faster charge transfer occurs in the low spin state of Co²⁺ sites (LS: t_2g⁶e_g¹), in which the formation of O* from OH* as the rate-determining step in OER can be accelerated for favorable OER. More importantly, the new monoclinic ABO₄-type material presented in this work is significantly different from the known spinel and perovskite oxides and may pioneer a new wave of research as efficient electrocatalysts and energy materials.