Self-supported N-doped carbon-coupled Ni–Co binary nanoparticle electrodes derived from bionic design of wood cell walls for durable overall water splitting†

Abstract

Designing high-performance, environmentally friendly, and durable bifunctional electrode materials for electrocatalytic water splitting is a key challenge in implementing sustainable energy technology. Here, we report a bionic modification of wood cell walls inspired by marine mussel adhesive proteins to develop a cost-effective yet high-efficiency wood-based bifunctional electrocatalyst. Ni–Co binary nanoparticles integrated with nitrogen-doped carbonized wood (Ni–Co/N@CW) were prepared by capitalizing on porous wood cell walls as confined spaces. Dopamine was adopted as an adhesive to achieve homogeneous dispersion of the nanoparticles, followed by forming graphitic carbon layers to encapsulate the nanoparticles through a calcination process. Structural and morphological studies revealed that the optimal Ni–Co/N@CW possesses a large surface area, abundant mesopores, and significant N doping in the carbonized wood framework, with 85% of pyridinic N. When employed as both the anode and cathode electrocatalyst in an alkaline medium, the cost-effective Ni–Co/N@CW catalyst manifests outstanding catalytic performance with low overpotentials and robust stability, surpassing the counterparts and recently reported earth-abundant electrocatalysts for both the oxygen evolution reaction (OER; overpotential of 290 mV at 10 mA cm⁻²) and hydrogen evolution reaction (HER; overpotential of 143 mV at 10 mA cm⁻²). Most notably, the as-prepared electrode achieves a current density of 10 mA cm⁻² at a comparatively low voltage of 1.60 V during overall water splitting in an alkaline electrolyzer. The hierarchically porous structures, advanced mass and charge transport ability (attributed to pyridinic N and graphitic C), and abundant active centers (Ni–Co binary metal sites) collectively unveil a synergistic effect that enhances the water-splitting catalytic activity of Ni–Co/N@CW, as revealed by a series of characterization studies and density functional theory (DFT) calculations. Additionally, the remarkable structural and chemical stability of the hierarchically porous Ni–Co/N@CW results in the (–) Ni–Co/N@CW‖Ni–Co/N@CW (+) water electrolysis cell displaying excellent long-term stability. The development of efficient and economic-friendly self-supported electrodes could contribute to the related energy-conversion systems and advance the progress of biomass-based devices.