Decoupled Electrochemical Water Splitting: From Fundamentals to Applications

TLDR

Electrolytic water splitting is a promising method for storing renewable energy as hydrogen and oxygen, but efficient production is limited by the difficulty of keeping the gases separated during intermittent operation. This review surveys recent advances in decoupled electrolysis for water splitting and examines its potential to enable other sustainable chemical processes. Decoupled electrolysis generates oxygen via mediator reduction and hydrogen via subsequent mediator reoxidation, allowing the gases to be produced at different times, rates, or in separate cells.

Abstract

Abstract Electrolytic water splitting to generate hydrogen and oxygen is one of the most promising ways in which to harness intermittent renewable power sources and store the energy these provide as a clean‐burning and sustainable fuel. In recent years, this has led to an explosion in reports on electrochemical water splitting, most of them focused on improving the efficiency of the electrochemical reactions themselves. However, efficient generation of hydrogen and oxygen is of little use if these products cannot be kept separate and the community is now coming to realize that there are considerable challenges associated with maintaining adequate separation between H 2 and O 2 during electrolysis driven by intermittent renewable sources. Decoupled electrolysis (whereby oxygen production occurs with reduction of a suitable mediator and hydrogen production is then paired with the reoxidation of this mediator) offers a solution to many of these challenges by allowing O 2 and H 2 to be produced at different times, at different rates, and even in completely different electrochemical cells. In this review, an overview of recent progress in the field of decoupled electrolysis for water splitting is given and the potential that this approach has for enabling a range of other sustainable chemical processes is explored.