Rational Design of Graphene‐Supported Single Atom Catalysts for Hydrogen Evolution Reaction

Abstract

The proper choice of nonprecious transition metals as single atom catalysts (SACs) remains unclear for designing highly efficient electrocatalysts for hydrogen evolution reaction (HER). Herein, reported is an activity correlation with catalysts, electronic structure, in order to clarify the origin of reactivity for a series of transition metals supported on nitrogen‐doped graphene as SACs for HER by a combination of density functional theory calculations and electrochemical measurements. Only few of the transition metals (e.g., Co, Cr, Fe, Rh, and V) as SACs show good catalytic activity toward HER as their Gibbs free energies are varied between the range of –0.20 to 0.30 eV but among which Co‐SAC exhibits the highest electrochemical activity at 0.13 eV. Electronic structure studies show that the energy states of active valence dz2 orbitals and their resulting antibonding state determine the catalytic activity for HER. The fact that the antibonding state orbital is neither completely empty nor fully filled in the case of Co‐SAC is the main reason for its ideal hydrogen adsorption energy. Moreover, the electrochemical measurement shows that Co‐SAC exhibits a superior hydrogen evolution activity over Ni‐SAC and W‐SAC, confirming the theoretical calculation. This systematic study gives a fundamental understanding about the design of highly efficient SACs for HER.

Engineering Local Coordination Environments of Atomically Dispersed and Heteroatom‐Coordinated Single Metal Site Electrocatalysts for Clean Energy‐Conversion

“…The activity–electronic structure relationship for a series of transition metal‐based MN 4 sites (Co, Fe, Ni, Mn, Mo, W, Pd, Ru, etc.) was studied by Hossain et al The DFT results reveal that the Δ G H* is highly related to the energy states of the d z 2 valence orbitals, and their resulting antibonding orbitals (σ*), after H adsorption. Higher energy levels of σ* induce a more unoccupied orbital, resulting in stronger adsorption of H* intermediates and vice versa.…”

“…Many non‐noble metal‐based SACs have also been synthesized that exhibited good HER activities, including NiN x , CoN x , NiC x , and graphdiyne‐supported Fe 0 /Ni 0 in acidic media, and both MoN 1 C 2 and WN 1 C 3 in alkaline media. The enhanced intrinsic activity should be ascribed to the unique coordination environment of the metal centers .…”

Densely Populated Single Atom Catalysts

“…The as‐prepared FeSA‐G showed an ORR performance similar to that of Pt/C but with a higher stability. Moreover, these nano structure substrates with high specific surface area have additional advantages: 1) It can maximize the accessibility of the high‐density single atom active sites on the exposed high area support surface; 2) Single atomic sites can be clearly characterized on simple ordered low‐dimensional structures, such as graphene, MoS 2 , and MXene, etc . Typically, to robustly immobilize the metal atoms on the support, the heteroatoms doping, defects, and vacancies are usually introduced into the support to form strong interaction with metal atoms.…”

Modulating the Electronic Structure of Single‐Atom Catalysts on 2D Nanomaterials for Enhanced Electrocatalytic Performance

“…Yang et al revealed that the higher ORR activity of FeN 4 than Pt/C originates from the Fe–pyrrolic–N configuration rather than Fe–pyridinic–N configuration by using DFT calculation . Hossain et al suggested the HER activity of MN 4 on graphene highly depends on the energy states of active valence d z 2 orbitals and their resulting antibonding state of metal center . The superior activity of CoN 4 sites could be attributed to its location of 3d z 2 valence orbital near to the Fermi level, together with the partially empty antibonding state, which can lead to an optimum adsorption strength toward hydrogen adsorption.…”