CoP Nanoframes as Bifunctional Electrocatalysts for Efficient Overall Water Splitting

Transition-metal phosphides have been shown to be promising electrocatalysts in water for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). To maximize reactivity toward both entails limiting the catalyst size while maintaining reactivity and avoiding aggregation. Frame-like hollow nanostructures (nanoframes) provide the required open structure with sufficient channels into the interior volume. We demonstrate here the design and synthesis of CoP nanoframes (CoP NFs) by a strategy involving precipitation, chemical etching, and low-temperature phosphidation steps. It results in impressive bifunctional catalytic activities for both HER and OER and consequently enables a highly efficient water electrolyzer with a current density of 10 mA cm–2 driven by a cell voltage of only 1.65 V. The strategy has been generalized for the preparation of nanoframe Co dichalcogenides CoX2 NFs, with X = S, Se, and Te. The results of electrochemical measurements, supported by density functional theory calculations, show that HER catalytic activities for the series follow the sequence: CoP NFs > CoSe2 NFs > CoS2 NFs > CoTe2 NFs.