Print Email Facebook Twitter Orientation of a bipolar membrane determines the dominant ion and carbonic species transport in membrane electrode assemblies for CO2reduction Title Orientation of a bipolar membrane determines the dominant ion and carbonic species transport in membrane electrode assemblies for CO2reduction Author Blommaert, M.A. (TU Delft ChemE/Materials for Energy Conversion and Storage) sharifian, rezvan (TU Delft ChemE/Transport Phenomena; Wetsus, European Centre of Excellence for Sustainable Water Technology) Shah, N. (TU Delft ChemE/Delft Ingenious Design) Nesbitt, N.T. (TU Delft ChemE/Materials for Energy Conversion and Storage) Smith, W.A. (TU Delft ChemE/Materials for Energy Conversion and Storage) Vermaas, D.A. (TU Delft ChemE/Transport Phenomena) Date 2021 Abstract 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 CO2 reduction, the BPM orientation determines the environment of the CO2 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 CO2 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. CO2 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 CO2 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 CO2 reduction. This journal is To reference this document use: http://resolver.tudelft.nl/uuid:e145076f-7c11-474e-aad1-94db4b4ae064 DOI https://doi.org/10.1039/d0ta12398f ISSN 2050-7488 Source Journal of Materials Chemistry A, 9 (18), 11179-11186 Part of collection Institutional Repository Document type journal article Rights © 2021 M.A. Blommaert, rezvan sharifian, N. Shah, N.T. Nesbitt, W.A. Smith, D.A. Vermaas Files PDF d0ta12398f.pdf 1.27 MB Close viewer /islandora/object/uuid:e145076f-7c11-474e-aad1-94db4b4ae064/datastream/OBJ/view