Orientation of a bipolar membrane determines the dominant ion and carbonic species transport in membrane electrode assemblies for CO 2 reduction.

Autor: Blommaert MA; Department of Chemical Engineering, Delft University of Technology 2629 HZ Delft The Netherlands d.a.vermaas@tudelft.nl., Sharifian R; Department of Chemical Engineering, Delft University of Technology 2629 HZ Delft The Netherlands d.a.vermaas@tudelft.nl.; Wetsus, European Centre of Excellence for Sustainable Water Technology 8911 MA Leeuwarden The Netherlands., Shah NU; Department of Chemical Engineering, Delft University of Technology 2629 HZ Delft The Netherlands d.a.vermaas@tudelft.nl., Nesbitt NT; Department of Chemical Engineering, Delft University of Technology 2629 HZ Delft The Netherlands d.a.vermaas@tudelft.nl., Smith WA; Department of Chemical Engineering, Delft University of Technology 2629 HZ Delft The Netherlands d.a.vermaas@tudelft.nl., Vermaas DA; Department of Chemical Engineering, Delft University of Technology 2629 HZ Delft The Netherlands d.a.vermaas@tudelft.nl.
Jazyk: angličtina
Zdroj: Journal of materials chemistry. A [J Mater Chem A Mater] 2021 Mar 11; Vol. 9 (18), pp. 11179-11186. Date of Electronic Publication: 2021 Mar 11.
DOI: 10.1039/d0ta12398f
Abstrakt: A bipolar membrane (BPM), consisting of a cation and an anion exchange layer (CEL and AEL), can be used in an electrochemical cell in two orientations: reverse bias and forward bias. A reverse bias is traditionally used to facilitate water dissociation and control the pH at either side. A forward bias has been proposed for several applications, but insight into the ion transport mechanism is lacking. At the same time, when implementing a BPM in a membrane electrode assembly (MEA) for CO 2 reduction, the BPM orientation determines the environment of the CO 2 reduction catalyst, the anolyte interaction and the direction of the electric field at the interface layer. In order to understand the transport mechanisms of ions and carbonic species within a bipolar membrane electrode assembly (BPMEA), these two orientations were compared by performing CO 2 reduction. Here, we present a novel BPMEA using a Ag catalyst layer directly deposited on the membrane layer at the vapour-liquid interface. In the case of reverse bias, the main ion transport mechanism is water dissociation. CO 2 can easily crossover through the CEL as neutral carbonic acid due to the low pH in the reverse bias. Once it enters the AEL, it will be transported to the anolyte as (bi)carbonate because of the presence of hydroxide ions. When the BPM is in the forward bias mode, with the AEL facing the cathode, no net water dissociation occurs. This not only leads to a 3 V lower cathodic potential but also reduces the flux of carbonic species through the BPM. As the pH in the AEL is higher, (bi)carbonate is transported towards the CEL, which then blocks the majority of those species. However, this forward bias mode showed a lower selectivity towards CO production and a higher salt concentration was observed at the cathode surface. The high overpotential and CO 2 crossover in reverse bias can be mitigated via engineering BPMs, providing higher potential for future application than that of a BPM in forward bias owing to the intrinsic disadvantages of salt recombination and poor faradaic efficiency for CO 2 reduction.
Competing Interests: There are no conflicts to declare.
(This journal is © The Royal Society of Chemistry.)
Databáze: MEDLINE
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