Curvature-switched activity of carbon nanotube-supported single atom catalysts for the hydrogen evolution reaction†

The hydrogen evolution reaction (HER) is an essential process for hydrogen production through water splitting. Atom-doped carbon nanotubes (CNTs) exhibit significant potential in promoting the electrocatalytic HER. By performing density functional theory (DFT) calculations, we have screened HER performance over a series of single atom transition metals (TM = Mo, Rh, Fe, Cr, Co, Zn, Mn, Cu, Ni, Pd) anchored on CNTs (n, n) (n = 5, 10) and graphene (seen as a CNT with the smallest curvature), and found the volcano curves between the adsorption free energy of H* (ΔG_H*) and the current density for the HER, yielding the RhN₄ catalyst at the peak of the volcano and even with a current density higher than that of Pt when the curvature is smaller than (10, 10). Then, more detailed DFT calculations were conducted to investigate the effect of curvature of CNTs on tuning the HER activity of RhN₄@CNT (n, n) (n = 5–10) catalysts, where ΔG_H* decreased with the decrease of the curvature, suggesting CNT-supported single atom catalysts having curvature-switched HER activity. The improved HER activity at a higher curvature arose from the more upshifted d-band center. Creating one single vacancy (5-1DB defect) could further enhance the HER activity of RhN₄@CNTs. Our work provides a novel approach to designing HER catalysts with tunable activity and stability.