Controlled Electrochemical Synthesis of Ag Nanoparticles and Their Morphology-Dependent Performances on Catalysing Hydrogen Evolution Reactions

Abstract

Hydrogen evolution reaction (HER) is one of the most critical reactions in fuel chemistry to produce clean and sustainable hydrogen gas as a renewable energy source. Nowadays, HER has always been catalysed with costly Pt or Pd metal1. To reduce the cost but still maintain a satisfactory performance, studies on Pt/Pd free catalysts for HER have never ceased. In the present work, we explore the electrodeposition of three morphologies (polyhedral, dendritic, and spherical) of Ag nanoparticles on boron-doped diamond electrodes (BDDEs) in various electrochemical conditions including deposition potential and deposition time. Specifically, by varying the deposition potentials of the single-stepped electrochemical deposition, a morphological change from polyhedral to homogeneous dendritic Ag was observed. The high deposition potential would drive the formation of dendritic Ag, which is a thermodynamically unfavourable structure with high surface energy. On the other hand, a two-stepped deposition mechanism was performed to synthesize spherical Ag nanoparticles. This two-stepped mechanism, which was used in synthesising small Au nanoparticles with high coverage by F. Bottari et al., contains a nucleation step at a more negative potential, and a growth step at a less negative potential.2 The sizes of each type of Ag nanoparticles were confirmed by Scanning Electron Microscopy (SEM), and the surface compositions were verified by X-Ray Photoelectron Spectroscopy (XPS). The current densities for HER catalysis were investigated using Linear Sweep Voltammetry (LSV), and a connection between morphologies and catalytic activities was drawn. All three types of Ag modified BDDEs showed better catalytic performance compared to that of drop-coated colloidal Ag-BDDE with comparable coverage and bare BDDE. Notably, spherical Ag-NP modified BDDE with an average particle diameter of 75nm has the highest percentage of pure elemental silver and showed the best performance as well as high stability in HER catalysis, which can be a less expensive yet efficient alternative for Pt/Pd containing catalysts.