Active Site Engineering in CoP@NC/Graphene Heterostructures Enabling Enhanced Hydrogen Evolution

Abstract

As the core of an electrocatalyst, the active site is critical to determine its catalytic performance in the hydrogen evolution reaction (HER). In this work, porous N-doped carbon-encapsulated CoP nanoparticles on both sides of graphene (CoP@ NC/GR) are derived from a bimetallic metal−organic framework (MOF)@graphene oxide composite. Through active site engineering by tailoring the environment around CoP and engineering the structure, the HER activity of CoP@NC/GR heterostructures is significantly enhanced. Both X-ray photoelectron spectroscopy (XPS) results and density functional theory (DFT) calculations manifest that the electronic structure of CoP can be modulated by the carbon matrix of NC/GR, resulting in electron redistribution and a reduction in the adsorption energy of hydrogen (ΔG H* ) from −0.53 to 0.04 eV. By engineering the sandwich-like structure, active sites in CoP@NC/GR are further increased by optimizing the Zn/Co ratio in the bimetallic MOF. Benefiting from this active site engineering, the CoP@NC/GR electrocatalyst exhibits small overpotentials of 105 mV in 0.5 M H 2 SO 4 (or 125 mV in 1 M KOH) to 10 mA cm −2 , accelerated HER kinetics with a low Tafel slope of 47.5 mV dec −1 , and remarkable structural and HER stability.

Integrated Heterogeneous Engineering with the Vacancy Defect of Porous CoPv-MoxPv Nanosheets for an Accelerated Hydrogen Evolution Reaction

“…Also, the two left peaks at 782.4 and 798.3 eV with two satellite peaks (Sat.) were attributed to oxidized Co species (Figure a) . For comparison, negative shifts (δ−) of Co 2p 3/2 and Co 2p 1/2 of Co–P in CoMo x P v /CNT-300 were observed (∼0.3 and ∼0.1 eV, respectively).…”

“…were attributed to oxidized Co species (Figure 3a). 39 For comparison, negative shifts (δ−) of Co 2p 3/2 and Co 2p 1/2 of Co−P in CoMo x P v /CNT-300 were observed (∼0.3 and ∼0.1 eV, respectively). The two broad peaks at ∼231 and ∼234 eV in Figure 3b correspond to the Mo 3d 5/2 and Mo 3d 3/2 states, respectively.…”

Compositional Engineering of Co(II)MOF/Carbon-Based Overall Water Splitting Electrocatalysts: From Synergistic Effects to Structure–Activity Relationships

“…Finally, the electrocatalytic activity for CoP@ NC/GR remained largely unchanged after 20 h of continuous HER testing in 0.5 M H 2 SO 4 at 20 mA cm −2 , meaning that the integration of GO strongly enhances the stability of CoP@ NC/GR. 98 On top of the pyrolysis, doping with S and N elements was used to replace P elements in a further discussion of the electrochemical properties. Zhang and co-workers employed an in situ growth strategy to anchor CoMOFs derived core−shell structures Co/Co 9 S 8 onto GO sheets and used them as precursors for pyrolysis at different temperatures.…”

“…The overpotential (105 mV) and Tafel slope (47.5 mV dec –1 ) of CoP@NC/GR were smaller than those of CoP and CoP@NC. Finally, the electrocatalytic activity for CoP@NC/GR remained largely unchanged after 20 h of continuous HER testing in 0.5 M H 2 SO 4 at 20 mA cm –2 , meaning that the integration of GO strongly enhances the stability of CoP@NC/GR . On top of the pyrolysis, doping with S and N elements was used to replace P elements in a further discussion of the electrochemical properties.…”

“…(e) The corresponding Tafel slope of material of the same series and 20% Pt/C during the HER process with 0.5 M H 2 SO 4 . Reproduced with permission from ref . Copyright 2021 American Chemical Society.…”