Abstract
Anion exchange membrane water electrolysis is an attractive technology for low-cost generation of “green” hydrogen by combining the use of noble metal-free catalysts with pure water feed. By thus addressing main drawbacks of the liquid alkaline electrolysis and proton exchange membrane water electrolysis, anion exchange membrane water electrolysis stands an excellent chance of replacing the two technologies. The development of active and stable platinum group metal (PGM)-free catalysts for oxygen evolution reaction (OER) is crucial for making anion exchange membrane water electrolyzers (AEMWEs) practical. Here, we synthesized, characterized and tested two La–Sr–Co oxide-based OER catalysts. First, we characterized the catalysts by XRD, SEM, and N2 physisorption and assessed their OER activity in a three-electrode cell. Next, we focused on electrode fabrication, demonstrating the importance of catalyst-ink application to the porous transport layers (PTLs) and a key role of adding a binder to the catalyst ink to prevent the catalyst detachment from the PTL in pure water. We tested three membrane electrode assemblies prepared using different formulations of the anode catalyst ink. The results show that the optimum ink formulation is essential for the performance on pure-water feed by maximizing OH− conductivity of the catalyst layer and catalyst-membrane interface.
| Original language | English |
|---|---|
| Article number | 232484 |
| Journal | Journal of Power Sources |
| Volume | 556 |
| DOIs | |
| State | Published - Feb 1 2023 |
Funding
An important aspect to be considered when testing alkaline MEA using with liquid feed streams such as KOH solutions and DI water is the order of testing. This issue was investigated previously by Lindquist et al. [27] and by Hassan et al. [58], who pointed out that rinsing with high quantities of DI water needs to be performed before switching from a supporting electrolyte feed to a DI water feed. The purpose of rinsing is to remove any residual OH− ions from the MEA, which can otherwise alter the ionic conductivity within the AEM and catalyst layers, resulting in a better cell performance. To further investigate the effect of residual OH− on cell performance, we recorded polarization curves in DI water for MEA#2 and MEA#3 at the end of the 20-h chronopotentiometric experiment (dash-dot line and diamond-symbol plots in Fig. 8c and d) and then again after tests with supporting electrolytes followed by flushing the cell with 2 L of DI water. These latter polarization curves are labeled as end-of-test (EOT) and marked with dashed lines and triangle symbols in Fig. 8c and d. The performance of MEA#2 after 20-h stability test shown in Fig. 8c is much worse than at BOL (ca. 140 mV at 500 mA cm−2). However, at EOT the performance recovers completely and it becomes even better at current densities greater than 500 mA cm−2 compared to that at BOL. This could be due to the presence of residual OH− ions in the MEA, as suggested by Lindquist et al. and Hassan et al. [27,58]. Another possibility is that the AEI could undergo degradation during testing, as indicated by Li et al. [17,25], causing loss of the OH−-conducing functional groups. This partial loss in OH− conductivity gets partially compensated by the flow of high pH electrolytes. The results in Fig. 8d for MEA#3 can be viewed as supporting the latter hypothesis. This MEA had a higher content of AEI than MEA#2 and showed much lower performance degradation during the 20-h stability test. Also in this case, the performance at EOT recovered completely, even at low current densities. These results suggest that since the anode of MEA#3 contains a higher amount of AEI, a lower fraction of the total ionomer degraded during the test compared to MEA#2. These results point to the crucial role of the ionic conductivity in the anode CL, dictated by the effectiveness of OH− conduction paths at the interface between AEI and the catalyst surface in AEMWE operating on pure water.Funding was provided by US DOE Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office, under the Electrocatalysis Consortium (ElectroCat), Dr. Dimitrios Papageorgopolous and Dr. David Peterson, Technology Managers. Research presented in this article was also supported by the Laboratory Directed Research and Development program of Los Alamos National Laboratory under project number 20210953PRD3. This work was authored in part by Los Alamos National Laboratory operated by Triad National Security, LLC under US DOE contract no. 89233218CNA000001 and by Oak Ridge National Laboratory operated by UT-Battelle, LLC, under contract no. DE-AC05-00OR22725. STEM research conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. Funding was provided by US DOE Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office, under the Electrocatalysis Consortium (ElectroCat) , Dr. Dimitrios Papageorgopolous and Dr. David Peterson, Technology Managers. Research presented in this article was also supported by the Laboratory Directed Research and Development program of Los Alamos National Laboratory under project number 20210953PRD3 . This work was authored in part by Los Alamos National Laboratory operated by Triad National Security, LLC under US DOE contract no. 89233218CNA000001 and by Oak Ridge National Laboratory operated by UT-Battelle, LLC, under contract no. DE-AC05-00OR22725. STEM research conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.
| Funders | Funder number |
|---|---|
| EOT | |
| Electrocatalysis Consortium | |
| U.S. Department of Energy | 89233218CNA000001 |
| Albert Ellis Institute | 17,25 |
| Office of Science | |
| Oak Ridge National Laboratory | DE-AC05-00OR22725 |
| Laboratory Directed Research and Development | |
| Los Alamos National Laboratory | 20210953PRD3 |
| Hydrogen and Fuel Cell Technologies Office | |
| Ministry of Economic Affairs | 27,58 |
Keywords
- Anion exchange ionomer
- Anion exchange membrane water electrolysis
- Oxygen evolution reaction
- PGM-Free
- Perovskite
