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.

Keywords: co‐electrolysis; electrooxidation of biomass; hybrid water electrolysis; hybrid water splitting; industrial scale; techno‐economic analysis; value‐added organic oxidation reaction.

Figure 1

Schematic illustration of hybrid water electrolysis systems showing cathodic hydrogen production on the left and anodic substrates (yellow) and their value‐added products (green) on the right.

Figure 2

Hydrogen production potential of different hybrid water electrolysis processes by the demand of the anodically produced organic products. For this estimation, the annual production of the value‐added chemicals from Table 2 was converted to mol and multiplied by the ratio of H₂ molecules produced per molecule of anodic product. Subsequently, the molar annual production potential of H₂ was converted back to Mt. If the product of the hybrid water electrolysis is the same for different processes, the feedstock is specified in brackets.

Figure 3

Scale of hydrogen production through hybrid water electrolysis compared to the global hydrogen demand. Methanol is currently produced thermocatalytically from syngas (H₂ and CO). Therefore, its production from methane would not only produce green hydrogen, but also prevent the H₂ consumption of the methanol synthesis. OOR (organic oxidation reactions) is the potential scale of H₂ production assuming that the current demand for all chemicals in Figure 2 is produced by hybrid water electrolysis. Data for the hydrogen demand is taken from the Global Hydrogen Report of the International Energy Agency 2022.^{[ 38 ]}