Unconventional bi-vacancies activating inert Prussian blue analogues nanocubes for efficient hydrogen evolution

Prussian blue analogues (PBA) have been explored as electrocatalyst for the hydrogen evolution reaction, however, they suffer from poor electrical conductivity and blocked active sites and thus usually operate at overpotentials drastically above thermodynamic requirement. Herein, we report a creation of unconventional anion (cyano group) and cation (cobalt) bi-vacancies to boost CoFe-PBA for HER through a rapid tannic acid (TA) etching strategy. The combined experimental and theoretical investigations indicate that the introduction of bi-vacancies would be favorable to exposure of accessible active sites, optimizing the electron density of CoFe PBA, and lowering the reaction energy barrier. As a result, the TA-etched CoFe PBA nanocubes supported on nickel foam (NF) (CoFe-PBA@TA/NF) exhibit outstanding HER catalytic activity with an overpotential of only 86 mV at 10 mA cm−2, which is not only significantly lower than bare PBA supported on NF (158 mV), but also comparable to the commercial Pt/C catalyst.