Challenges for Hybrid Water Electrolysis to Replace the Oxygen Evolution Reaction on an Industrial Scale

Abstract

To enable a future society based on sun and wind energy, transforming electricity into chemical energy in the form of fuels is crucial. This transformation can be achieved in an electrolyzer performing water splitting, where at the anode, water is oxidized to oxygen—oxygen evolution reaction (OER)—to produce protons and electrons that can be combined at the cathode to form hydrogen—hydrogen evolution reaction (HER). While hydrogen is a desired fuel, the obtained oxygen has no economic value. A techno‐economically more suitable alternative is hybrid water electrolysis, where value‐added oxidation reactions of abundant organic feedstocks replace the OER. However, tremendous challenges remain for the industrial‐scale application of hybrid water electrolysis. Herein, these challenges, including the higher kinetic overpotentials of organic oxidation reactions compared to the OER, the small feedstock availably and product demand of these processes compared to the HER (and carbon dioxide reduction), additional purifications costs, and electrocatalytic challenges to meet the industrially required activities, selectivities, and especially long‐term stabilities are critically discussed. It is anticipated that this perspective helps the academic research community to identify industrially relevant research questions concerning hybrid water electrolysis.

In-Liquid Plasma-Mediated Manganese Oxide Electrocatalysts for Quasi-Industrial Water Oxidation and Selective Dehydrogenation

“…However, to drive both OER and selective organic oxidation efficiently, developing active, stable (both mechanical and chemical), inexpensive, and earth-abundant electrocatalysts is essential and of utmost importance. 8 Since the discovery of biological water oxidation associated with the photosystem II (PSII), Mn has gained significant attention as an OER central metal for artificial photosynthesis because of its suitable redox behavior in the catalytic process. 9−12 However, most of the commonly used synthetic Mn-oxide-based catalysts require a large overpotential to generate high OER current density and deactivate rather quickly under long-term assessment, making them industrially unsuitable as compared to other transition metal (e.g., Ni, Co, Fe) oxide catalysts.…”

“…The HER kinetics can be accelerated either by introducing highly active OER catalysts or by replacing the OER process with the oxidation of protic organic compounds, which indeed decreases the required cell potentials dramatically and maximizes the energetic efficiency. − The overall reaction becomes economically more beneficial when a selective value-added oxidized product is generated instead of a low-value oxygen. However, to drive both OER and selective organic oxidation efficiently, developing active, stable (both mechanical and chemical), inexpensive, and earth-abundant electrocatalysts is essential and of utmost importance …”

Water-soluble nickel and iron salts for hydroxymethylfurfural (HMF) and water oxidation: the simplest precatalysts?

“…Fossil fuels and petrochemicals must be replaced by carbon-neutral alternatives to stop climate change and close the carbon cycle. 1 The most promising alternatives are hydrogen and hydrocarbons produced electrocatalytically through water or carbon dioxide reduction, respectively. 2–4 These (cathodic) reduction reactions require protons and electrons that are supplied by their (anodic) oxidative counterpart.…”

“…This anodic counterpart can be the oxygen evolution reaction (OER) or an organic oxidation reaction (OOR, hybrid water splitting). 1 The OER has the advantage that only water is required as substrate; thus, it can be applied on a large scale. 1,5 However, the OER produces no value-added compound.…”

“…1 The OER has the advantage that only water is required as substrate; thus, it can be applied on a large scale. 1,5 However, the OER produces no value-added compound. The advantage of organic oxidation reactions is that they require thermodynamically less energy and can be value-added, e.g.…”