A novel flower-like architecture of FeCo@NC-functionalized ultra-thin carbon nanosheets as a highly efficient 3D bifunctional electrocatalyst for full water splitting

Abstract

A novel three-dimensional (3D) hierarchically meso/macroporous flower-like architecture of ultra-thin N-doped carbon nanosheets (NCNS) with fine FeCo@NC core–shell units dispersed on their surfaces (denoted as FeCo@NC/NCNS) is reported as an efficient catalyst for two key electrode processes (i.e. the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) in the development of sustainable energy conversion systems. Upon optimization of the dosages of Fe/Co sources and calcination temperature, the optimal Fe_0.5Co_0.5@NC/NCNS-800 sample exhibits high activity with a potential of 1.5 V vs. reversible hydrogen electrode (RHE) to achieve a current density of 10 mA cm⁻² for the OER in 1.0 M KOH, which even surpassed that of commercial RuO₂. Moreover, as an HER electrocatalyst in 1.0 M KOH, Fe_0.5Co_0.5@NC/NCNS-800 just requires a low overpotential of 150 mV to achieve 10 mA cm⁻² with an onset potential of −63 mV. All these results highlight the synergistic effects of the 3D macroporous channels of the flower-like architecture, 2D mesoporous CNSs, high specific surface area, fine FeCo@NC core–shell units, and various active centers for boosting the OER/HER catalytic activities, defining the Fe_0.5Co_0.5@NC/NCNS as one of the best non-precious metal-based carbonaceous electrocatalysts for oxygen/hydrogen-based electrocatalysis. More importantly, when Fe_0.5Co_0.5@NC/NCNS was used as positive and negative electrodes in a two-electrode system for overall water splitting, it just required a cell voltage of 1.60 V to achieve ∼10 mA cm⁻², which opens a new possibility for the construction of novel water splitting devices. We also believe that our present synthetic strategy can encourage further research for the development of other 3D hierarchically meso/macroporous noble-metal-free catalysts for sensors, batteries, and various other renewable energy applications without any tedious steps or templates.