Ni- and P-doped carbon from waste biomass: A sustainable multifunctional electrode for oxygen reduction, oxygen evolution and hydrogen evolution reactions

Abstract

High performance electrocatalysts based on nickel nanoparticles and biomass derived carbon were fabricated via a sustainable, inexpensive synthetic route utilizing waste carrot as a naturally occurring carbon precursor containing abundant amounts of phosphorus and oxygen. The electrocatalytic performance of the fabricated electrodes with variable nickel mass loadings (0 ̶ 30 wt%) was investigated. For Ni mass loading of 19.3 wt%, the resulting Ni/P-doped carbon exhibits optimum catalytic activity for oxygen reduction (ORR), oxygen evolution (OER) and hydrogen evolution reaction (HER). The electrocatalyst reveals onset and half-wave potentials of 0.81 and 0.67 V vs. reversible hydrogen electrode (RHE), and a kinetic limiting current density of 13.66 mA cm−2 at 0.1 V vs. RHE for ORR. The material exhibits modest Tafel slopes of 67.6 and 134.9 mV dec−1 and overpotentials of 368 and 297 mV to reach a current density of 10 mA cm−2 for OER and HER, respectively. The results on the composite physicochemical characteristics, electrochemically active surface area, ionic conductivity and ionic diffusivity reveal a sustainable process to fabricate eco-friendly, trifunctional electrocatalysts having high efficiency.