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 Ni₂W₄C-W₃C Janus structures with abundant Ni–W metallic bonds on surfaces through interfacial engineering. Inserting Ni atoms into the W₃C crystals in reaction progress generates a new Ni₂W₄C phase, making the inert W atoms in W₃C be active sites in Ni₂W₄C for overall water splitting. The Ni₂W₄C-W₃C/carbon nanofibers (Ni₂W₄C-W₃C/CNFs) require overpotentials of 63 mV to reach 10 mA cm⁻² for hydrogen evolution reaction (HER) and 270 mV to reach 30 mA cm⁻² 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⁻², respectively. Density functional theory (DFT) results indicate that the strong interactions between Ni and W increase the local electronic states of W atoms. The Ni₂W₄C provides active sites for cleaving H–OH bonds, and the W₃C facilitates the combination of H_ads intermediates into H₂ 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.