Controlling palladium morphology in electrodeposition from nanoparticles to dendrites via the use of mixed solvents.

Haytham E M Hussein,Richard Beanland,Ben G Breeze,Julie V Macpherson,Houari Amari

doi:10.1039/d0nr05630h

Abstract

By changing the mole fraction of water (χwater) in the solvent acetonitrile (MeCN), we report a simple procedure to control nanostructure morphology during electrodeposition. We focus on the electrodeposition of palladium (Pd) on electron beam transparent boron-doped diamond (BDD) electrodes. Three solutions are employed, MeCN rich (90% v/v MeCN, χwater = 0.246), equal volumes (50% v/v MeCN, χwater = 0.743) and water rich (10% v/v MeCN, χwater = 0.963), with electrodeposition carried out under a constant, and high overpotential (-1.0 V), for fixed time periods (50, 150 and 300 s). Scanning transmission electron microscopy (STEM) reveals that in MeCN rich solution, Pd atoms, amorphous atom clusters and (majority) nanoparticles (NPs) result. As water content is increased, NPs are again evident but also elongated and defected nanostructures which grow in prominence with time. In the water rich environment, NPs and branched, concave and star-like Pd nanostructures are now seen, which with time translate to aggregated porous structures and ultimately dendrites. We attribute these observations to the role MeCN adsorption on Pd surfaces plays in retarding metal nucleation and growth.

Highlights

Monitoring changes in the position and intensity of bands in the different Raman regions as a function of χwater can be used as a diagnostic for how inter- and intra-solvent bonding interactions change.[38,39,40]
As water content increases both the CuN and C–H bands shift to a higher wavenumber and the intensity decreases
We demonstrate the versatility of electron transparent boron-doped diamond (BDD) electrodes for making combined electrochemical and high resolution Scanning transmission electron microscopy (STEM) measurements of metal electrodeposition

Summary

Introduction

In electrochemical devices used for energy conversion, nanostructures such as nanoparticles (NPs), made of metals, for example the platinum group metals, control the electrocatalysis process.[1,2,3] The electrocatalytic reaction can be optimised by careful control of the metal catalyst crystal structure, size, loading, presence of defects etc.[4,5,6,7,8,9] The need to produce effective electrocatalysts has led to the exploration of many different chemical and physical NP and nanostructure synthesis strategies.[2,10,11] These include chemical vapour deposition, atomic layer deposition, colloidal synthesis, sputtering etc.[12,13,14,15,16] Palladium (Pd) is an interesting metal due to its use in Electrodeposition offers an interesting route for nanomaterial production, as it is effectively bottom-up synthesis, lends itself to scalability, and does not require sophisticated instruments or a high technical level of training.[18,19,20,21,22] Electrodeposition offers a wide variety of tuneable parameters for controlling nanostructure morphology, these include e.g. electrode deposition potential and time of deposition, temperature, and electrolyte composition.[23,24,25,26] It is not surprising that electrodeposition has been used to make a variety of controlled Pd nanostructures such as nanowires,[17] cubes, nanoflowers, nanoframes, and high index faceted Pd nanocrystals.[11,27,28,29]

Results

Discussion

Conclusion