Boettcher, ShannonChen, Lihaokun2024-03-252024-03-252024-03-25https://hdl.handle.net/1794/29273Water dissociation (WD, H2O → H+ + OH−) is the core process in bipolar membranes (BPMs) that limits energy efficiency. Both electric-field and catalytic effects have been invoked to describe WD, but the interplay of the two and the underlying design principles for WD catalysts remain unclear. Furthermore, how WD is driven by voltage and catalyzed is not understood. In Chapter II, by using precise layers of metal-oxide nanoparticles, membrane-electrolyzer platforms, materials characterization, and impedance analysis, we illustrate the role of electronic conductivity in modulating the performance of WD catalysts in the BPM junction through screening and focusing the interfacial electric field and thus electrochemical potential gradients. In contrast, the ionic conductivity of the same layer is not a significant factor in limiting performance. BPM water electrolyzers, optimized via these findings, use ~30-nm-diameter anatase TiO2 as an earth-abundant WD catalyst, and generate O2 and H2 at 500 mA cm−2 with a record-low total cell voltage below 2 V. These advanced BPMs might accelerate deployment of new electrodialysis, carbon-capture, and carbon-utilization technology. In Chapter III, we report BPM electrolyzers with two reference electrodes to measure temperature-dependent WD current and overpotential (ηwd) without soluble electrolyte. Using TiO2-P25-nanoparticle catalyst and Arrhenius-type analysis, Ea,wd was 25–30 kJ/mol, independent of ηwd, with a pre-exponential factor proportional to ηwd that decreases ~10-fold in D2O. We propose a new WD mechanism where metal-oxide nanoparticles, polarized by the BPM-junction voltage, serve as proton i) acceptors (from water) on the negative-charged side of the particle to generate free OH−, ii) donors on the positive-charged side to generate H3O+, and iii) surface conductors that connect spatially separate donor/acceptor sites. Increasing electric-field with ηwd orients water for proton-transfer, increasing the pre-exponential factor, but is insufficient to lower Ea.This dissertation includes previously published and unpublished co-authored materials.en-USAll Rights Reserved.bipolar membranecatalysiskineticsmechanismwater dissociationwater electrolysisElectronic Thesis or Dissertation