Pd surface functionalization of 3D electroformed Ni and Ni-Mo alloy metallic nanofoams for hydrogen production

IntroductionIn the case of hydrogen production through water electrolysis, one of the main targets is to develop more active cathodic materials, in order to optimize the efficiency of hydrogen evolution reaction (HER) and,... [ view full abstract ]

Introduction

In the case of hydrogen production through water electrolysis, one of the main targets is to develop more active cathodic materials, in order to optimize the efficiency of hydrogen evolution reaction (HER) and, consequently, enhance the overall energy efficiency of electrolysis. Thus, to develop suitable HER electrocatalysts either an increase of the electrode active surface area or a design of a material having high intrinsic catalytic activity should be taken into consideration, both of them decreasing the HER overpotential.

The paper presents some experimental results regarding the functionalization of 3D electroformed Ni and Ni-Mo alloy nanofoams  with Pd nanoclusters, as potential cathodic materials suitable for HER during water electrolysis.

Methods

The electrodeposition from aqueous electrolytes containing NiCl₂ and NH₄Cl has been applied to prepare the 3D Ni nanofoams. Ni-Mo (15-60 wt.% Mo) alloys have been electrodeposited involving either aqueous ammonium citrate type electrolytes or deep eutectic solvents based on choline chloride (DESs). Pd surface functionalization has been performed using both electroless and electrochemical procedures. To assess the HER efficiency against the Pd content characteristics, linear voltammetry, cyclic voltammetry and chronoamperometry techniques have been applied.

Results and Discussion

The electroformed Ni nanofoams usually showed a porous structure having macropores of about 20-30 µm and micropores of 3-5 µm,  with  a nodular growth, leading to a cauliflower-like morphology. The use of DESs to electrodeposit porous  Ni-Mo alloys facilitated the formation of a nanoporous structure associated with a cracks network as the molybdenum species content in the electrolyte increased. Depending on the applied procedure and the operation conditions, the content of the deposited Pd varied in the range of 0.35 – 3 wt.% (Fig.1). Depending on the porous structure characteristics of the metallic foams and Pd loading, Tafel slopes values between 65-150 mV.dec^-1 have been determined in natural sea water. A comparative analysis based on the determined Tafel slope values and hydrogen production rate vs. the applied current against the alloy deposit characteristics is presented, too.

  Acknowledgements: The authors acknowledge Executive Agency for Higher Education, Research, Development and Innovation Funding, for the funding under NANOFOAM project 37/2016, M Era Net Program.