Impact of Catalyst Reconstruction on the Durability of Anion Exchange Membrane Water Electrolysis

Abstract

Anion exchange membrane water electrolysis (AEMWE) offers an opportunity to use inexpensive nonprecious metal catalysts. However, pure water-fed AEMWE still faces issues of durability. Herein, we compared the stability of AEMWE under different anolytes, including KOH, pure water, and a phosphate buffer (PB) using a NiFeCo oxygen evolution reaction catalyst. Upon thoroughly characterizing several changes before/after 100 h durability tests, such as the cell performance, catalyst dissolution, catalyst morphologies, impedance of the anion exchange membrane, and catalytic layer, we speculate that the change of the local pH is the main factor causing catalyst reconstruction, which further leads to the loss of cell performance in the pure water-fed mode. By using PB to control the local pH, the morphology of the catalyst will no longer change after the durability test, and the cell performance can recover to the initial performance in pure water. These results not only indicate that the catalyst structural transformation is the main reason for the deactivation of pure water-fed AEMWE but also help find a way to achieve highly durable pure water-fed AEMWE.

Benchmarking the pH–Stability Relationship of Metal Oxide Anodes in Anion Exchange Membrane Water Electrolysis

“…These suggest that few dissolved Fe in the electrolyte can stabilize the catalyst. The above results reveal that the alkaline conditions enhance the OER kinetics, leading the overpotential to be lower than the critical value to maintain the stability of Fe species …”

“…The above results reveal that the alkaline conditions enhance the OER kinetics, leading the overpotential to be lower than the critical value to maintain the stability of Fe species. 21 To further investigate the possibility of metal oxides in the pure water AEMWE, we attempted a pre-activation approach that was previously reported in many studies. 38,46 One advantage of pre-activation is to promote surface reconstruction, which can improve the catalytic activity by exposing more active sites.…”

“…For example, why some state-of-the-art alkaline oxygen evolution reaction (OER) catalysts (e.g., NiFeO x ) are difficult to maintain stability in pure water. 21 To our knowledge, although many works have reported the application of TMOs in the AEMWE, the detailed pH response on catalytic and structural stability has not been studied. 22 Herein, we benchmarked the pH−stability relationship of four typical metal oxides (i.e., Ni/Co/Fe-based TMOs and IrO 2 ) as anode catalysts in the AEMWE.…”

Key components and design strategy of the membrane electrode assembly for alkaline water electrolysis

“…Recently, Lei et al investigated the impact of electrocatalyst reconstruction on the durability of pure water-fed AEMWE with a NiFeCo-based anode catalyst. 313 For the KOH feeding mode, the cell voltage of the AEMWE could maintain stability for 100 h at a current density of 200 mA cm −2 . The surface of reconstructed electrocatalysts lost contact with the ionomer, but could still participate in the reaction due to the contact with the KOH solution.…”

Anion Exchange Membrane Water Electrolysis: The Future of Green Hydrogen

“…But, since it is known that the catalyst structure, morphology, etc. can change during OER, this type of catalyst would need to be carefully characterized after (or when possible, during) OER to reveal its true active form. Lastly, Figure d shows a plot of η 10 as a function of apparent stability, taken from chronopotentiometric (CP) experiments with oxide, hydroxide, phosphide, and sulfur-decorated catalysts .…”