(419b) Atomically Dispersed Ni–Nx Species Anchored Porous Carbon with Embedded Ni Nanoparticles for Efficient Hydrogen Evolution

Abstract: exploring earth-abundant, active and stable electrocatalysts to replace noble metal materials for hydrogen evolution reaction (HER) through alkaline water electrolysis system is key to the development of sustainable energy conversion technologies. Here, we report a novel hybrid electrocatalyst comprised of atomically dispersed Ni–N_x species anchored porous carbon (Ni−N−C) matrix with embedded Ni nanoparticles (NP) (Ni NP|Ni-N-C). Benefiting from the high surface area and strong coupling interaction of the Ni NP and Ni−N−C, the achieved Ni NP|Ni-N-C/EG hybrid electrode displays excellent electrocatalytic activity for HER in basic condition with a low overpotential of 147 mV to reach current density of 10 mA cm^−2. The overpotential for the Ni NP|Ni-N-C/EG is well comparable to the best reported value in literature for all existing heteroatom-doped nanocarbon catalysts and even lower than those reported for other transition-metal-based compounds in basic media. Furthermore, the Ni NP|Ni-N-C/EG hybrid electrode exhibits outstanding catalytic activity for overall-water-splitting under alkaline condition, as reflected by delivering a current density of 10 mA cm^−2 at 1.58 V, which surpasses that of the benchmark combination catalyst (Ir/C (anode)-Pt/C (cathode), 1.60 V at 10 mA cm^−2) for sufficiently high overpotentials. For the first time, we demonstrate an efficient alkaline hydrogen evolution on atomically dispersed Ni–N_x species in porous carbon electrocatalysts by accelerating water dissociation kinetics, in which the presence of Ni nanoparticles can optimize the surface states of Ni−N_x active centers and reduce the energy barriers of dissociated water molecules, synergistically improving the OH^− adsorption towards promoted HER kinetics. Electrochemical results, coupled with the thiocyanate poisoning experiments, HAADF-STEM analyses, XPS analysis, as well as the EXAFS and XANES results, reveal that the hybridization of atomically dispersed Ni–N_x active centers with that of embedding Ni NP modulates the electronic structure and facilitates electron transfer at the constructed interface, which synergistically boost the HER performance of Ni NP|Ni-N-C. Theoretical calculations manifest that the incorporation of Ni NP into atomically dispersed Ni−N−C frameworks can effectively promote initial water dissociation process (Volmer step) and simultaneously optimize the OH^− adsorption free energy on the Ni NP|Ni-N-C, resulting in the improved kinetics of the HER in alkaline solutions.