Cobalt Incorporation Promotes CO₂ Desorption from Nickel Active Sites Encapsulated by Nitrogen-Doped Carbon Nanotubes in Urea-Assisted Water Electrolysis

The potential application prospects of urea-assisted water electrolysis toward hydrogen production in renewable energy infrastructure can effectively alleviate energy shortages and environmental pollution caused by rich urea wastewater. It is of prominent significance that adjusting the CO₂ desorption of nickel-based electrocatalysts can overcome the slow reaction kinetics for urea oxidation reaction (UOR) to achieve exceptional catalytic activity. In this work, cobalt (Co) metal doping is employed to boost the UOR performance of nitrogen-doped carbon nanotubes encapsulating nickel nanoparticle electrocatalysts (Ni@N-CNT). The influence of diverse Co doping concentrations on the performance of UOR and hydrogen evolution reaction (HER) catalytic activities associated with stability are systematically investigated. The Co dopant can effectively promote the dynamical conversion of Ni to Ni³⁺ species; as a result, the UOR catalytic activity is improved by 1.8-fold at 1.6 V vs RHE. The DFT calculation results show that the CoNi bimetallic structure possesses a comparably lower binding energy for CO₂ adsorption accelerating the rate-limiting step. Meanwhile, the Co dopant also boosts the HER performance, achieving a 57 mV reduction in overpotential at 100 mA cm^-2 due to the creation of more active sites. In addition, the assembled urea-assisted water electrolysis attains 10 mA cm^-2 at merely 1.51 V as well as excellent stability.