In-situ transformation to accordion-like core-shell structured metal@metallic hydroxide nanosheet from nanorod morphology for overall water-splitting in alkaline media

Exploring highly-efficient, low-cost and earth-abundant bi-functional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have a key role in economical overall water-splitting. Herein, a facile and general route is developed to prepare various non-noble metal-based electrocatalysts via NH₃⋅H₂O treatment (NT) on Ni foam (NF) (M-NT/NF, M = Co, Ni, Fe, Mn, Cu). The morphology and compositions of the obtained catalysts could be tuned via solvothermal process with NH₃⋅H₂O, and then optimizing the active sites exposure and effectively change the reaction kinetics of the electrocatalytic reaction. Moreover, the substrate of Ni foam is in favor of electrolyte transfer and release of produced gases. Then, the obtain Co-NT/NF, composed of metallic Co and Co(OH)₂, exhibits excellent catalytic performance for HER with low overpotential of 178 mV@10 mA cm^-2 and small Tafel slope of 75 mV dec^-1, which is rarely reported for HER. For OER, only a low overpotential of 226 mV is required to deliver 10 mA cm^-2 with a small Tafel slope of 46 mV dec^-1. Moreover, the reported electrocatalysts present negligible current density loss during long-term stability measurement, demonstrating robust nanostructure feature of the prepared catalysts. This work opens a facile and efficient avenue to design bi-funtional electrocatalyst coupling with outstanding catalytic performance.