Nickel/Nickel Oxide-Nitrogen Self-Doped Carbon Nanosheets for Electrocatalytic Oxygen and Hydrogen Evolution Reactions

The search for bifunctional electrocatalysts with low cost and high efficiency to drive the development of water splitting is essential for sustainable energy conversion. In this work, a simple two-step biomass-assisted impregnation–calcination strategy was adopted to prepare a series of porous nickel/nickel oxide-nitrogen self-doped carbon (Ni/NiO-NC) nanosheet composites using waste corn stalks (CSs) as a multifunctional template, reductant, and carbon and nitrogen sources. The contents of carbon, nickel, and nickel oxide components can be adjusted by varying the calcination temperature and CS amount. When they are applied as electrocatalysts in the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), the optimal Ni/NiO-NC nanosheet obtained at 300 °C and 1.00 g of CS displays the best OER and HER activities in 1.0 M KOH media with low overpotentials of 293 and 179 mV at 10 mV cm^–2, small Tafel slopes of 141 and 111 mV dec^–1, respectively, and good stability. Furthermore, a water electrolyzer is also fabricated by utilizing cheap nonprecious Ni/NiO-NC-300 as both OER and HER catalysts to investigate the water-splitting performance. This as-reported simple, environmental, and cheap strategy could be extended to develop other two-dimensional transition-metal-based nanosheet electrocatalysts for a high-performance water-splitting reaction.