Decoupled Electrolysis Based on Pseudocapacitive Auxiliary Electrodes: Mechanism and Enhancement Strategies

Abstract

Hydrogen is the way for connecting the renewable energy plants and consumers. However, achieving cheap, widespread hydrogen production and storage is complicated task. For hydrogen production the alkaline and acidic membrane electrolysers are used most widely. The membrane electrolysers have their limits, for example high standard potential of water splitting reaction, moderate efficiency, high cost and low durability. Decoupling oxygen evaluation reaction (OER) and hydrogen evaluation reaction (HER) is promising strategy to avoid using of membrane. Water electrolysis in separate cells was reported in 2017 by A. Landman et al., reaching the efficiency of 58% [1].In 2022, we reported for the first time the amphoteric decoupled electrolysis by combining acid and alkaline cells [2]. The efficiency was enhanced due to reduced standard potential for water splitting by realizing HER in acidic environment but OER in alkaline. For maintaining decoupled amphoteric electrolysis, we connected acid and alkaline cell with the primary Pt electrodes and pseudocapacitive auxiliary electrodes (AE). For acid cell the AE electrode based on WO3 was used while for the alkaline cell electrodes based on Ni(OH)2. In proposed electrolyser two separate working cycles can be distinguished – different chemical processes occur at different polarities applied between primary Pt electrodes. The potential for gas generation depends on the polarity of the applied potential due to different chemical processes. In both polarities, hydrogen and oxygen are generated in separate cells. At the first cycle, ions are diffusing into the AEs and gases are generated with the Faradaic efficiency of 98 % and energetical efficiency of 43 %. At the second cycle, ions are released from AEs and gasses are generated with the Faradaic efficiency of 98 % and energetical efficiency of 201 %, providing the total energetical efficiency for whole operation of 71 %.Herein we will discuss the effect of acid OER catalyst or the structure and composition of AEs on the performance of decoupled electrolysis, illuminating the pathways for bringing this concept as the main strategy for water splitting.