Enhanced Electron Penetration through an Ultrathin Graphene Layer for Highly Efficient Catalysis of the Hydrogen Evolution Reaction

Abstract

Major challenges encountered when trying to replace precious-metal-based electrocatalysts of the hydrogen evolution reaction (HER) in acidic media are related to the low efficiency and stability of non-precious-metal compounds. Therefore, new concepts and strategies have to be devised to develop electrocatalysts that are based on earth-abundant materials. Herein, we report a hierarchical architecture that consists of ultrathin graphene shells (only 1-3 layers) that encapsulate a uniform CoNi nanoalloy to enhance its HER performance in acidic media. The optimized catalyst exhibits high stability and activity with an onset overpotential of almost zero versus the reversible hydrogen electrode (RHE) and an overpotential of only 142 mV at 10 mA cm(-2) , which is quite close to that of commercial 40 % Pt/C catalysts. Density functional theory (DFT) calculations indicate that the ultrathin graphene shells strongly promote electron penetration from the CoNi nanoalloy to the graphene surface. With nitrogen dopants, they synergistically increase the electron density on the graphene surface, which results in superior HER activity on the graphene shells.

Catalytic impact of alloyed Al on the corrosion behavior of Co50Ni23Ga26Al1.0magnetic shape memory alloy and catalysis applications for efficient electrochemical H2generation

“…Several studies on CoNi alloys report performance of submicron size powder electrodes, 22 porous foams, 23 or even encapsulating CoNi nanoalloys in ultrathin layers of graphene. 24 Unlike other attempts to replace precious-metal-based electrocatalysts of HER, lowering efficiency and stability of such compounds, CoNi@C fabricated by Deng et al 24 are claimed to possess high performance. The optimized catalyst exhibits high stability and activity with an onset overpotential of almost zero versus the reversible hydrogen electrode (RHE) and an overpotential of only 142 mV at 10 mA cm À2 , which is quite close to that of commercial 40% Pt/C catalysts.…”

Apically Dominant Mechanism for Improving Catalytic Activities of N-Doped Carbon Nanotube Arrays in Rechargeable Zinc-Air Battery

“…1e), which agrees well with the (111) crystal plane of CoNi alloy. 17 TEM elemental mapping shows that N and C signals are uniformly distributed within carbon nanotubes, whereas Co and Ni signals are only detected at the black-contrast apical domains in the upper carbon nanotube sections. These findings suggest that nitrogen element is doped into the carbon nanotubes, and the metal NPs within the carbon nanotubes are comprised of Co and Ni elements.…”

“…We hypothesize that the alloyed CoNi NPs 8 within the CoNi@NCNT/NF may have synergistic effects that further improve nitrogen dopant catalytic activity. 17 To better understand the effect of apical dominance for improving the catalytic activity of NCNT arrays, we proposed a mechanistic model to illustrate the electrochemical process on CoNi@NCNT/NF and NCNT/NF electrodes, respectively. A typical schematic diagram of the CoNi@NCNT/NF electrode is illustrated in Fig.…”

Design Strategies toward Advanced MOF‐Derived Electrocatalysts for Energy‐Conversion Reactions

“…[64,81] Generally speaking, metal NPs embedded in carbon shells cannot only increase electron transport, but also change the local work function for tuning the adsorption of intermediates. [64,82] For example, the pioneering work reported by Deng et al indicated that CoNi NPs coated by ultrathin graphene shells (carbon layers < 3) enabled enhanced electron penetration from the metal cores to the carbon shells, thereby modulating the electron density and the electronic structure of the graphene surface. [82] This effect further tuned free energy for the adsorption of intermediates to enhance catalytic activity.…”

“…[64,82] For example, the pioneering work reported by Deng et al indicated that CoNi NPs coated by ultrathin graphene shells (carbon layers < 3) enabled enhanced electron penetration from the metal cores to the carbon shells, thereby modulating the electron density and the electronic structure of the graphene surface. [82] This effect further tuned free energy for the adsorption of intermediates to enhance catalytic activity. At the same time, their study demonstrated the synergistic effect between N dopants and enclosed metal clusters for further enhanced activity.…”