ZrCo3B2 and HfCo3B2 Electrodes Go on Stage for Oxygen Evolution Reaction.

The water electrolysis is one of the key processes for producing hydrogen-a clean and sustainable energy carrier. However, its wide application onto the industrial scale still lack of the long-lasting and highly efficient electrocatalysts for the kinetically sluggish oxygen evolution reaction (OER). Here, we demonstrate the OER performance of intermetallic precursors TMCo3B2 (TM = Zr, Hf) in the bulk state allowing to avoid the detrimental effects of binders and/or supports and assess the intrinsic activity and stability of electrode material. Significantly lower OER overpotentials for TMCo3B2 (ca. 270 mV) compared to elemental Co (ca. 320 mV), almost doubled current density values at maximum potential of 1.95 V vs. RHE (0.7 A cm-2 for ZrCo3B2 and 1.1 A cm-2 for HfCo3B2) as well as the stability of their OER activity for almost 500 h reaction period bring forward those intermetallic compounds among other known electrocatalysts. Furthermore, our results prominently illustrate the importance of crystal structures and chemical bonding of intermetallic compounds, remarkably influencing the OER performance. These highly OER active and stable ZrCo3B2 and HfCo3B2 electrodes will pave the way for usage of intermetallic compounds in the large-scale electrolyzer applications.