Anodic Reactions in Alkaline Hybrid Water Electrolyzers: Activity versus Selectivity

Abstract

Affordable and abundant sources of green hydrogen can give a large impetus to the Energy Transition. While conventional water electrolysis has positioned itself as a prospective candidate for this purpose, it lacks cost competitiveness. Hybrid water electrolysis (HWE) has been praised for its ability to address the issues of conventional water electrolysis due to its decreased energy requirements and its ability to generate value‐added products, among other advantages. In this perspective, we discuss the challenges related to the applicability of HWE, using the glycerol oxidation reaction as an example, and we identify pitfalls often found in the literature. Reported catalysts, especially those based on abundant materials, suffer from a severe selectivity‐activity tradeoff, hampering their industrial applicability due to large costs associated with product separation and purification. Additionally, testing electrocatalysts under conditions that are relevant for their applications is encouraged, yet these conditions are largely unknown, as in‐depth knowledge of the catalytic mechanisms is largely missing. Lastly, an opportunity to increase the amount of interdisciplinary research concerning both the engineering requirements and financial performance of HWE is discussed. Increased focus on these objectives may boost the development of HWE on an industrial scale.

Metal–organic frameworks (MOFs) for hybrid water electrolysis: structure–property–performance correlation

“…(iii) Faradaic efficiency Faradaic efficiency in electrocatalytic AORs measures the effectiveness of producing desired products relative to the consumed charge. [70][71][72][73] It indicates how efficiently the electrocatalytic process forms desired products while minimizing unwanted by-products. High faradaic efficiency means most of the consumed charge contributes to desired product formation, maximizing yield and selectivity while minimizing side reactions.…”

“…MOFs have garnered considerable attention in recent years due to their unique properties and potential applications in different AORs. [68][69][70]77 MOFs can serve as promising catalysts in these reactions due to their high surface area, tunable porosity, and ability to incorporate different metal centers with varied catalytic activities. 32,33,36,80 Most of the MOFs developed for AORs are based on the various transition metal ions like cobalt, iron, nickel, and copper.…”