Electrodeposition and Characterization of Nanocrystalline Ni-Mo Catalysts for Hydrogen Production

J Halim,A Waheed,S El-Raghy,R Abdel-Karim,M Nabil

doi:10.1155/2012/845673

Abstract

Ni-Mo nanocrystalline deposits (7–43 nm) with a nodular morphology were prepared by electrodeposition using direct current from citrate-ammonia solutions. They exhibited a single Ni-Mo solid solution phase. The size of the nodules increased as electroplating current density increased. The molybdenum content—estimated using EDX analysis—in the deposits decreased from about 31 to 11 wt% as the current density increased from 5 to 80 mA·cm−2. The highest microhardness value (285 Hv) corresponded to nanodeposits with 23% Mo. The highest corrosion resistance accompanied by relatively high hardness was detected for electrodeposits containing 15% Mo. Mo content values between 11 and 15% are recommended for obtaining better electrocatalytic activity for HER.

Highlights

Ni-Mo deposits have been well known for their use as cathodes for hydrogen production from water by electrolysis as well as catalysts for hydrogen production by steam reforming of hydrocarbons [1].Arul Raj and Venkatesan [2] showed an increased electrocatalytic effect of Ni-Mo electrodeposited alloys for the hydrogen evolution reaction than that showed by nickel and other nickel-based binary alloys such as Ni-Co, Ni-W, Ni-Fe, and Ni-Cr
The mechanism of induced codeposition of molybdenum with nickel involves an adsorbed Ni-Mo reaction intermediate (2). In this case, [Ni(Cit)MoO2]ads acts as a surfaceadsorbed intermediate, while citrate acts as a ligand connecting both Ni2− and MoO2− together
By increasing the current density, the reduction rate of Ni2− ions is increased giving no chance for the surface adsorbed intermediate to be formed, gaining less chance for Mo to be codeposited with Ni, and this leads to a reduction in the Mo content in the Ni-Mo alloys at high current densities [21]

Summary

Introduction

Arul Raj and Venkatesan [2] showed an increased electrocatalytic effect of Ni-Mo electrodeposited alloys for the hydrogen evolution reaction than that showed by nickel and other nickel-based binary alloys such as Ni-Co, Ni-W, Ni-Fe, and Ni-Cr. In addition, Ni-Mo alloys are considered as highly corrosion resistant due to the good corrosion protection characteristics of molybdenum in nonoxidizing solutions of hydrochloric, phosphoric, and hydrofluoric acid at most concentrations and temperatures and in boiling sulfuric acid up to about 60% concentration [3]. RF magnetron sputtering, mechanical alloying, and electrodeposition techniques are employed in the production of nanocrystalline Ni-Mo alloys. Huang et al [5] reported that these alloys prepared by RF magnetron sputtering technique were to be promising electrodes for hydrogen evolution reactions. Nanocrystalline Ni-Mo alloys have been successfully produced using mechanical alloying method according to Kedzierzawski et al [6], indicating the positive contribution of the large surface area in increasing the catalytic effect as electrodes for hydrogen production and decreasing the exchange current density

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