Transition Metal Foams as Electrocatalysts for Hydrogen Evolution Reaction

Alkaline water electrolysis is a promising method for large-scale hydrogen production. In order to improve the energy efficiency of current alkaline electrolyzers, the development of new electrocatalytic materials for the hydrogen electrode is of paramount importance. Noble metal alloys are known to possess good catalytic activity towards the hydrogen evolution reaction (HER) but their high price and low availability prevents them to be considered for practical applications.

Nickel (Ni) and its alloys are relatively low-cost materials and have been shown to present good electrocatalytic activity for the HER, making these Ni-based electrodes the most usual choice for industrial applications in alkaline media [1]. The amount of the electrocatalytic material can be further reduced by using Ni alloys with a porous structure, which provide high surface areas while lowering the cost.

In this study, transition metal 3D nanoporous foams based on Ni, copper (Cu), and cobalt (Co) alloys are produced on stainless steel substrates by galvanostatic electrodeposition using hydrogen bubble evolution as a dynamic template [2]. The metallic foams are obtained from acidic sulfate-based solutions by applying current densities of 1 or 1.8 Acm^-2 and deposition times between 60 and 180 s.

The surface morphology of the metal foams was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) was used for the determination of their chemical composition. X-ray diffraction (XRD) was used to examine the crystallographic structure of the deposited metallic foams.

SEM analysis revealed that they have a nanostructured morphology consisting of micrometric pores with dendritic walls. The morphology (pore and dendrite size) and chemical composition were related to the deposition parameters.

The produced transition metal foams were evaluated as electrodes for HER in alkaline media. Chronoamperometry (CA) and linear scan voltammetry (LSV) were used to study the HER at the Ni/Cu/Co electrocatalysts in 8 M KOH solutions for temperatures ranging from 25 to 85 ºC.

The analysis of the obtained polarization curves enabled the determination of the main kinetic parameters, namely Tafel coefficients, charge transfer coefficients, exchange current densities and activation energies, allowing a direct comparison of the studied electrodes performances for the HER. The obtained parameters were also compared to that of single Ni and other Ni-based alloys.

The results suggest that these transition metal foams can be used to attain reasonably high HER efficiencies while using very low metal amounts. Moreover, these 3D electrocatalysts are produced using a low cost, one-step fabrication method that presents several advantages over conventional procedures.

References

1. D. Pletcher, X. Li, Prospects for alkaline zero gap water electrolysers for hydrogen production, Int. J. Hydrogen Energy 36 (2011) 15089.
2. H.C. Shin, J. Dong, M. Liu, Nanoporous structures prepared by an electrochemical deposition process. Adv. Mater. 15 (2003) 1610.