Challenges for Hybrid Water Electrolysis to Replace the Oxygen Evolution Reaction on an Industrial Scale
Authors: Kahlstorf Till , Hausmann Niklas , Menezes Prashanth 
Published: December 2024

To enable a future society based on sun and wind energy, the transformation of electricity into chemical energy in form of fuels is crucial. Electrolysis offers a promising solution, achieving this transformation by splitting water. At the anode, the oxygen evolution reaction (OER) produces protons and electrons that are used at the cathode for the hydrogen evolution reaction (HER) to generate hydrogen fuel. While hydrogen is the desired product, oxygen has limited economic value. From a techno-economic standpoint, a more attractive approach is hybrid water electrolysis, which replaces the OER with value-added oxidation reactions of abundant organic feedstocks.
However, significant challenges stand in the way of widespread adoption of hybrid water electrolysis for large-scale industrial applications. This work provides a critical analysis of these hurdles, delving deeper into each aspect:
Higher Kinetic Overpotentials for Organic Oxidation Reactions: Compared to the well-established OER, organic oxidation reactions generally have a lower energy consumption, but generally necessitate greater overpotentials to overcome kinetic limitations. Addressing this challenge requires the development of novel electrocatalysts that can significantly reduce the activation energy for organic oxidation reactions, bringing their kinetic performance closer to that of the OER.
Limited Availability and Product Demand of Feedstocks and Products: The organic feedstocks suitable for these reactions may be less abundant or have a lower market demand compared to hydrogen (or even CO2 reduction). This scarcity or limited economic value of the organic substrates and products can potentially hinder the overall economic viability of hybrid water electrolysis. Extensive research into utilizing readily available and sustainable organic feedstocks is crucial. Additionally, exploring and developing markets for the products generated from these oxidation reactions would be necessary for widespread adoption.
Additional Purification Needs: The products formed during organic oxidation reactions might require further purification steps to meet the specifications required for downstream applications. These additional purification processes add complexity and increase the cost associated with hybrid water electrolysis. Developing selective electrocatalysts that generate the desired products in high purity could significantly alleviate this challenge.
High Activity: The catalysts should possess a high intrinsic activity for the target organic oxidation reactions, ensuring fast reaction rates and maximizing product yield.
Selectivity for the Desired Products: Indiscriminate oxidation of the organic feedstock can lead to the formation of undesired byproducts, reducing the efficiency and necessitating complex downstream separations. Therefore, catalysts with high selectivity for the targeted products are essential.
Long-Term Stability: Electrocatalysts must maintain their activity and selectivity over extended periods under operating conditions. Degradation of the catalysts can occur due to various factors, including chemical and structural transformations during operation. Developing electrocatalysts with exceptional long-term stability is paramount for the practical application of hybrid water electrolysis.
By outlining these challenges, we aim to stimulate discussion and guide research efforts within the academic community. Addressing these critical aspects is essential to pave the way for the successful implementation of hybrid water electrolysis at an industrial scale, ultimately enabling a sustainable energy future.
Kahlstorf, J. N. Hausmann, T. Sontheimer, P. W. Menezes, Challenges for Hybrid Water Electrolysis to Replace the Oxygen Evolution Reaction on an Industrial Scale. Global Challenges 2023, 7, 2200242.

Figure 1