Transition metal phosphides (TMPs) 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 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 (DFT) calculations, show that HER catalytic activities for the series follow the sequence: CoP NFs > CoSe2 NFs > CoS2 NFs > CoTe2 NFs.

As the terminal step in photosystem II, and a potential half-reaction for artificial photosynthesis, water oxidation (2H₂O → O₂ + 4e^- + 4H⁺) is key, but it imposes a significant mechanistic challenge with requirements for both 4e^-/4H⁺loss and O—O bond formation. Significant progress in water oxidation catalysis has been achieved recently by use of single-site Ru metal complex catalysts such as [Ru(Mebimpy)(bpy)(OH₂)]²⁺[Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy = 2,2^′-bipyridine]. When oxidized from to Ru^V = O³⁺, these complexes undergo O—O bond formation by O-atom attack on a H₂O molecule, which is often the rate-limiting step. Microscopic details of O—O bond formation have been explored by quantum mechanical/molecular mechanical (QM/MM) simulations the results of which provide detailed insight into mechanism and a strategy for enhancing catalytic rates. It utilizes added bases as proton acceptors and concerted atom–proton transfer (APT) with O-atom transfer to the O atom of a water molecule in concert with proton transfer to the base (B). Base catalyzed APT reactivity in water oxidation is observed both in solution and on the surfaces of oxide electrodes derivatized by attached phosphonated metal complex catalysts. These results have important implications for catalytic, electrocatalytic, and photoelectrocatalytic water oxidation.