In situ interfacial engineering of nickel tungsten carbide Janus structures for highly efficient overall water splitting.

Regulating chemical bonds to balance the adsorption and disassociation of water molecules on catalyst surfaces is crucial for overall water splitting in alkaline solution. Here we report a facile strategy for designing NiWC-WC Janus structures with abundant Ni-W metallic bonds on surfaces through interfacial engineering. Inserting Ni atoms into the WC crystals in reaction progress generates a new NiWC phase, making the inert W atoms in WC be active sites in NiWC for overall water splitting. The NiWC-WC/carbon nanofibers (NiWC-WC/CNFs) require overpotentials of 63 mV to reach 10 mA cm for hydrogen evolution reaction (HER) and 270 mV to reach 30 mA cm for oxygen evolution reaction (OER) in alkaline electrolyte, respectively. When utilized as both cathode and anode in alkaline solution for overall water splitting, cell voltages of 1.55 and 1.87 V are needed to reach 10 and 100 mA cm, respectively. Density functional theory (DFT) results indicate that the strong interactions between Ni and W increase the local electronic states of W atoms. The NiWC provides active sites for cleaving H-OH bonds, and the WC facilitates the combination of H intermediates into H molecules. The in situ electrochemical-Raman results demonstrate that the strong absorption ability for hydroxyl and water molecules and further demonstrate that W atoms are the real active sites.