Recent Progress on Copper‐Based Electrode Materials for Overall Water‐Splitting

Abstract

Exponential increase in fossil fuel consumption demands an immediate alternative for a sustainable development. Furthermore, fossil fuel combustion releases a large quantity of CO 2 every day. In the quest for an alternative, although hydrogen is found to be a potent fuel with zero carbon waste, bulk-scale hydrogen production via steam reforming or partial oxidation of hydrocarbons produces tons of CO and CO 2 as waste. Perhaps, hydrogen production by means of electrocatalytic water splitting remains a viable and less energy-intensive approach. However, the potential bottlenecks of the water splitting are the large thermodynamic barrier and sluggish kinetics of the oxygen evolution reaction (OER) associated with the hydrogen evolution reaction (HER), a comparatively straight-forward reaction. Efforts over the last few decades have made it possible to design very reactive noble-metal-based catalysts, using Pt, IrO 2 , and RuO 2 , which dramatically diminish the working potential and enhance the rate of water oxidation. Nonetheless, the scarcity of these rare-earth metals precludes their physical implication and leads to the design of active transition-metal catalysts like CoO x and FeNi(O)OH as key alternatives. However, copper, a highly conductive and one of the earth's most abundant metals, has not much been explored for electrode materials. Lately, copper-based materials have been employed as successful catalysts for not only the OER and HER (individual half-cell reactions), but also for overall water splitting (OWS) through the design of bifunctional copper catalysts. This review summarizes the recent developments of copper-based electrode materials for electrocatalytic water splitting, with emphasis on OER, HER, and OWS studies. Moreover, Cu materials are categorized by means of counter anions present and based on their catalytic activity (mono-and/ or bi-functional behavior). Future scope and challenges to develop active Cu-based materials, as non-noble and earth abundant catalysts for sustainable energy studies, are highlighted.

Electrochemically Derived Crystalline CuO from Covellite CuS Nanoplates: A Multifunctional Anode Material

“…4 Additionally, it may interfere in contributing to the higher feasible overpotential compared to the thermodynamic potential. 3,5 Thus, building an efficient electrocatalyst for OER is the need of the hour. As an efficient catalyst, rutile-structured RuO 2 and IrO 2 have been considered as a benchmark due to their outstanding activity, stability, 6−8 and the presence of surface oxygen species that controlled the activity-controlling parameters.…”

Air‐Stable Mn doped CuCl/CuO Hybrid Triquetrous Nanoarrays as Bifunctional Electrocatalysts for Overall Water Splitting

“…After the HER reaction, the valence state of Cu does not change much, combined with the performance of CuCl (Figure S11), the active site can be attribute to the CuCl. In contrast, even with similar triquetrous structure, the commercial CuCl‐NF displays a much higher voltage and a slight decrease in stability when given a same current density (50 mA cm −2 , Figure S10), suggesting the presence of CuO component in the hybrid play a significant role for the stabilization of active CuCl as well as the synergetic effect between the CuO and CuCl [48] . All these factors give rise to the excellent activity and good stability of the as designed CuCl/CuO(Mn)‐NF electrode.…”

Recent Developments on Cr‐Based Electrocatalysts for the Oxygen Evolution Reaction in Alkaline Media

“…Functional electrocatalysts based on cheaper first‐row transition metals such as nickel (Ni), cobalt (Co), iron (Fe) and, manganese (Mn) etc. are finding increasing importance and adoption in electrochemical devices operating in an alkaline environment [8–11] . Among the d‐group metal catalysts, Ni‐based oxides and hydroxides are regarded as one of the best economic alternatives for water splitting applications [11,12] .…”

“…are finding increasing importance and adoption in electrochemical devices operating in an alkaline environment. [8][9][10][11] Among the d-group metal catalysts, Ni-based oxides and hydroxides are regarded as one of the best economic alternatives for water splitting applications. [11,12] However, the shortcomings of a single-metal centre for catalysis demands the association of a co-catalyst.…”