Ultrathin Prussian blue analogue nanosheet arrays with open bimetal centers for efficient overall water splitting

Direct construction of Prussian blue analogues (PBAs) nanosheets arrays as a bifunctional electrocatalyst for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of great significance but still remains challenging. Herein, for the first time, we have proposed an efficient strategy to synthesize Co–Fe bimetallic PBA nanosheet arrays with ultrathin feature and open bimetal centers via one-pot coprecipitation reaction of nickel nitrate and sodium nitroferricyanide in the presence of nickel foam. When employed as the self-supporting bifunctional electrocatalyst, the optimized PBA nanosheet arrays require overpotentials of only 256 and 48 mV to drive 10 mA cm−2 for OER and HER in 1.0 M KOH, respectively. Remarkably, it allows an alkali-electrolyzer with 10 mA cm−2 at a low cell voltage of 1.545 V and a robust operation stability of no less than 36 h. The combination of experimental results and theoretical calculation analysis unravelled that such exceptional electrocatalytic performances could be traced to the ultrathin nanosheet, porous surface structure, and coordinately unsaturated metal centers, enabling abundant active sites, accelerated mass/charge transfer capability, as well as the favorable energy for their transformation to high active Co/Fe-based (oxy)hydroxides during water electrolysis. More broadly, the synthetic strategy is versatile and can be applied to achieve copper foam- and titanium foam-supported bifunctional CoFe-PBA nanosheet electrocatalysts.