Open AccessThe Role of Water in Vapor-fed Proton-Exchange-Membrane Electrolysis
Author(s) -
Julie C. Fornaciari,
Michael R. Gerhardt,
Jie Zhou,
Yagya N. Regmi,
Nemanja Danilovic,
Alexis T. Bell,
Adam Z. Weber
Publication year - 2020
Publication title -
journal of the electrochemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.258
H-Index - 271
eISSN - 1945-7111
pISSN - 0013-4651
DOI - 10.1149/1945-7111/ab9b09
Subject(s) - electrolysis , water vapor , anode , chemistry , cathode , relative humidity , electrolysis of water , polymer electrolyte membrane electrolysis , water transport , mole fraction , analytical chemistry (journal) , electrode , chemical engineering , environmental engineering , thermodynamics , environmental chemistry , water flow , organic chemistry , electrolyte , environmental science , physics , engineering
Water-vapor fed electrolysis, a simplified single-phase electrolyzer using a proton-exchange membrane electrode assembly, achieved >100 mA cm −2 performance at <1.7 V, the best for water-vapor electrolysis to date, and was tested under various operating conditions (temperature and inlet relative humidity (RH)). To further probe the limitations of the electrolyzer, a mathematical model was used to identify the overpotentials, local water activity, water content values, and temperature within the cell at these various conditions. The major limitations within the water-vapor electrolyzer are caused by a decreased water content within the membrane phase, indicated by increased Ohmic and mass transport losses seen in applied voltage breakdowns. Further investigations show the water content ( λ , mole of water/mole of sulfonic acid) can decrease from 13 at low current densities down to 6 at high current densities. Increasing the temperature or decreasing RH exacerbates this dry-out effect. Using our mathematical model, we show how these mass transport limitations can be alleviated by considering the role of water as both a reactant and a hydrating agent. We show that low cathode RH can be tolerated as long as the anode RH remains high, showing equivalent performance as symmetric RH feeds.