W-induced morphological modification of NiFe layered double hydroxides as efficient electrocatalysts for overall water splitting

Highlights: • W-induced NiFe layered double hydroxides (LDHs) with controllable morphologies on carbon fiber papers are one-step fabricated. • 5 mM W doping modulates smooth NiFe hydroxide films to well-aligned NiFeW-LDHs. • The modulated NiFeW-LDHs exhibit a more than four-fold electrochemically surface area increase. • Remarkably enhanced oxygen evolution reaction and hydrogen evolution reaction performances are demonstrated. -- Abstract: Layered double hydroxides (LDHs) are one of the most efficient electrocatalysts for water splitting due to their nanosheet features and compositional flexibilities. This work explored the impact of W precursor concentration (0 ∼ 10 mM) on LDH morphologies and performance in hydrogen production. Using an electrodeposition W-doping process, W-induced NiFe LDHs (NiFeW-LDHs) were in-situ grown on carbon fiber papers for water splitting. A performance peak was found at a W doping of 5 mM with well-aligned nanosheets, which not only boosted the charge transfer ability and gas evolution but also offered more than a four-fold electrochemical surface area increase compared to film-like NiFe hydroxides. The NiFeW-LDHs exhibited remarkable performance compared to NiFe hydroxides, showing decreased overpotentials of 31 mV and 114 mV for the oxygen evolution reactions (OERs) and hydrogen evolution reactions (HERs) at 10 mA/cm² and -10 mA/cm², respectively, in alkaline media. The performance enhancement at 5 mM W-doping was linked to the well-aligned NiFeW-LDH nanosheets; smaller, less-textured nanosheets were observed with lower or higher W precursor concentrations (2.5 mM or >7.5 mM), leading to inferior OER and HER performances. Hence, an appropriate W doping is crucial to generating the morphologies that contribute to the higher performance of NiFeW-LDHs.