Upcycling red brick into a superior monolithic hydrogen evolution electrocatalyst

Abstract

Harvesting endogenous active metals from natural and even waste materials to develop efficient water splitting electrocatalysts is highly promising to achieve a sustainable H₂ economy. Herein, fired red brick (RB), a universal building material throughout history without any other utilization purposes, is converted into a superior monolithic electrocatalyst for the H₂ evolution reaction (HER) via successive chemical vapor deposition (CVD) and low-temperature phosphidation methods. During CVD and phosphorization processes, the endogenous Fe species within RB efficiently catalyze the growth of N,P-codoped carbon nanotubes (N,P-CNTs) from melamine pyrolysis, leading to the formation of high-density and well-interconnected Fe-encapsulated N,P-CNTs that are firmly embedded throughout the entire RB substrate (Fe@N,P-CNTs/RB) with high conductivity, excellent mechanical strength, and uniformly distributed active sites. The as-fabricated Fe@N,P-CNTs/RB can be directly used as a monolithic electrode for the HER in a 0.5 M H₂SO₄ solution, requiring overpotentials of 223.6 and 285.6 mV to reach current densities of −10 and −100 mA cm⁻², respectively, and exhibiting an exceptional stability for 100 h at −10 mA cm⁻² with an overpotential increase of only 69.7 mV.