Local ionic transport enables selective PGM-free bipolar membrane electrode assembly

Mengran Li; Eric W Lees; Wen Ju; Siddhartha Subramanian; Kailun Yang; Justin C Bui; Hugo-Pieter Iglesias van Montfort; Maryam Abdinejad; Joost Middelkoop; Peter Strasser; Adam Z Weber; Alexis T Bell; Thomas Burdyny

doi:10.1038/s41467-024-52409-z

Local ionic transport enables selective PGM-free bipolar membrane electrode assembly

Nat Commun. 2024 Sep 19;15(1):8222. doi: 10.1038/s41467-024-52409-z.

Authors

Mengran Li^#^{1

2}, Eric W Lees^#^{3

4}, Wen Ju^#^{5

6}, Siddhartha Subramanian⁷, Kailun Yang⁷, Justin C Bui^{8

9}, Hugo-Pieter Iglesias van Montfort⁷, Maryam Abdinejad^{7

10}, Joost Middelkoop⁷, Peter Strasser⁵, Adam Z Weber³, Alexis T Bell^{8

9}, Thomas Burdyny¹¹

Affiliations

¹ Department of Chemical Engineering, Delft University of Technology; 9 van der Maasweg, Delft, 2629HZ, the Netherlands. aaron.li1@unimelb.edu.au.
² Department of Chemical Engineering, The University of Melbourne, Melbourne, VIC, 3010, Australia. aaron.li1@unimelb.edu.au.
³ Energy Technologies Area, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
⁴ Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, BC, V6T 1Z3, Canada.
⁵ Chemical Engineering Division, Department of Chemistry, Technical University Berlin, Berlin, 10623, Germany.
⁶ Department of Electrochemistry and Catalysis, Leibniz Institute for Catalysis, 18059, Rostock, Germany.
⁷ Department of Chemical Engineering, Delft University of Technology; 9 van der Maasweg, Delft, 2629HZ, the Netherlands.
⁸ Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
⁹ Department of Chemical and Biological Engineering, University of California Berkeley, Berkeley, CA, 94720, USA.
¹⁰ Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
¹¹ Department of Chemical Engineering, Delft University of Technology; 9 van der Maasweg, Delft, 2629HZ, the Netherlands. t.e.burdyny@tudelft.nl.

^# Contributed equally.

Abstract

Bipolar membranes in electrochemical CO₂ conversion cells enable different reaction environments in the CO₂-reduction and O₂-evolution compartments. Under ideal conditions, water-splitting in the bipolar membrane allows for platinum-group-metal-free anode materials and high CO₂ utilizations. In practice, however, even minor unwanted ion crossover limits stability to short time periods. Here we report the vital role of managing ionic species to improve CO₂ conversion efficiency while preventing acidification of the anodic compartment. Through transport modelling, we identify that an anion-exchange ionomer in the catalyst layer improves local bicarbonate availability and increasing the proton transference number in the bipolar membranes increases CO₂ regeneration and limits K⁺ concentration in the cathode region. Through experiments, we show that a uniform local distribution of bicarbonate ions increases the accessibility of reverted CO₂ to the catalyst surface, improving Faradaic efficiency and limiting current densities by twofold. Using these insights, we demonstrate a fully platinum-group-metal-free bipolar membrane electrode assembly CO₂ conversion system exhibiting <1% CO₂/cation crossover rates and 80-90% CO₂-to-CO utilization efficiency over 150 h operation at 100 mA cm^-2 without anolyte replenishment.