Sustainable Processing of Ultralow-Cost Petroleum Cokes Into Ultrastable Self-Doped Fe3C@CNT Catalysts for High-Efficiency HER

Abstract

Petroleum cokes are largely used as low-cost anodes in aluminum industries and general fuels in cement industries, where large amounts of CO₂ are generated. To reduce CO₂ release, it is challenging to develop green strategies for processing abundant petroleum cokes into high-value products, because there are abundant hetero-atoms in petroleum cokes. To overcome such issues, a sustainable electrochemical approach is proposed to convert ultralow-cost high sulfur petroleum coke and iron powders into high-efficiency catalysts for hydrogen evolution reaction (HER). During molten-salt electrolysis, raw petroleum cokes are converted into CNTs via heteroatom removal and the catalytic effect of Fe, forming Fe₃C nanoparticles on the sulfur and nitrogen co-dopped carbon nanotubes (Fe₃C@S, N-CNTs). The electrochemical reaction analysis using the continuum model suggested that the rate-determining step referred to the slow transport of mobile ions inside the porous cathode. Because the self-doped S and N atoms massively alleviated the energy barrier for H^* absorption and H₂ desorption (i.e., promoting HER kinetics), the as-prepared Fe₃C@S, N-CNTs exhibited low overpotentials at 10 mA cm⁻² in acidic (96 mV) and alkaline (106 mV) solutions with ultralong-term duration (200 h). This study offers a sustainable approach to convert ultralow-cost petroleum cokes into ultrastable catalysts for high-efficiency HER.