Speakers
Description
The H2O molecule is omnipresent in electrochemistry, yet, beyond its role as solvent, its direct impact on catalyst activity, selectivity and deactivation remain poorly understood. Conversely, interfacial H2O reactivity is one of the focus subjects of the newly founded Interfacial Ionics Group.
In the first part of the poster, we discuss our findings on inner-sphere water dissociation and water formation (H2O ↔ H+ + OH-) over metal oxide nanoparticle surfaces inside bipolar membrane (BPM) junctions. By performing Tafel and Arrhenius analysis, we show that not only water dissociation can be catalysed, as has been shown previously, but also the reverse process of interfacial water formation. Strikingly, we observe a transition of varying Ea to a region of constant Ea with applied overpotential. This strongly indicates that active water dissociation and formation catalysts are maintained in their reversible state up to 100’s mA$\cdot$cm-2. We combine our experimental findings with Multiphysics simulations to develop an experimentally verifiable model about the BPM junction that avoids commonly made assumptions. Last, we use our insights to demonstrate BPM fuel cells, that operate the HOR in acidic and ORR in alkaline conditions.
In the second part, we focus on the role of interfacial water during the electrochemical ammonia oxidation reaction (AOR, 2NH3 + 6OH- ↔ N2 + 6H2O + 6e-). By releasing the stored H+, here in the form of H2O, green NH3 could serve a green hydrogen-carrier. However, the AOR suffers from high overpotentials and rapid catalyst deactivation, the origin of which is still being debated in the literature. We study the influence of OH- and H2O on the AOR activity and deactivation mechanism of polycrystalline Pt. In absence of OH- but in the presence of H2O, we observe strongly increasing overpotentials for NH3 decomposition, indicating inhibited water dissociation or formation on the NHx-covered Pt surface. Extensive Pt deactivation studies indicate (i) two potential-dependent N and NO deactivation processes in aqueous media, the latter being closely linked to the potential-dependent OH adsorption on Pt, (ii) suppression of NO but remaining N poisoning with decreasing H2O concentration and (iii) potential-dependent N-stripping to N2 in H2O-free conditions and stable NH3 decomposition. Our findings highlight the crucial role of OH- adsorption and water dissociation in NH3 oxidation and layout new pathways for more efficient and stable electrochemical NH3 oxidation in the future.
| Abstract Number (department-wise) | ISC 12 |
|---|---|
| Department | ISC (Roldán) |
