108 Search Results

As anion exchange membrane systems have emerged as a competitive low temperature electrolysis technology, research has expanded to other components and device integration. In this study, nickel (Ni) and stainless steel (SS)-based porous transport layers (PTLs) are investigated in membrane electrode assemblies (MEAs). Compared to MEAs using Ni, the SS PTL shows higher performance due to less kinetics and residual loss and possibly due to a combination of iron mobility improving oxygen evolution reactivity and electron conduction pathways, as well as higher porosity increasing site access. Voltage decay rates of approximately 144 and 115 μV/h, respectively, for the Ni andmore » SS PTLs are found, although the long-term durability and lifetime implications are convoluted. Voltage breakdown analysis confirms that both PTLs saw significant increases in residual loss possibly due to catalyst/PTL property changes that affected electronic, ionic, and mass transport pathways. For the Ni PTL, a higher proportion of the losses were due to cell kinetics; comparatively, more of the SS PTL losses were due to increases in the high frequency resistance. The experimental findings presented here provide insights on the impact of the PTL materials and their properties.« less

Pt-based electrocatalysts are effective for the hydrogen evolution reaction (HER); however, their limited ability to facilitate water dissociation and suboptimal hydrogen binding energy (H_BE) in alkaline electrolytes result in slow reaction kinetics, which hinders their cost-efficiency and practical applications. This study reports the synthesis of Co₂P-Pt heterostructure nanorods using a seed-mediated growth method, producing a high density of Co₂P-Pt interfacial sites. Density functional theory (DFT) calculations indicate that electronic interactions at these interfaces optimize H_BE on Pt, while the interfacial sites promote water dissociation. The Co₂P-Pt nanorods demonstrate an overpotential of 14 mV at 10 mA cm⁻² for the HER,more » highlighting the potential of precisely engineered metal-metal phosphide interfaces for enhancing electrocatalytic efficiency.« less

It is widely understood that the durability and reliability of polymer electrolyte membrane (PEM) water electrolyzers are heavily dependent on feedwater purity, with cation contaminants that originate from incomplete water purification and balance of plant materials significantly harming electrolyzer performance. However, contamination remains a challenge and a common cause of failure at the stack level, indicating the need for strategies to recover the performance of contaminated cells. In this study, we investigate the effects of temperature on the uptake, electrochemical impacts, and removal of contaminant calcium and iron cations. Lower operating temperatures increase the sensitivity of the cell performance tomore » contaminant cations, while also decreasing cation uptake and promoting contaminant removal. Computational charge transfer modelling shows that lower temperature increases the concentration of contaminant at the cathode and facilitates their removal from the cell. By testing single cells under scenarios designed to mimic stack temperature dynamics, we investigate low-temperature operation as an approach to stack-relevant contaminant recovery. Together, these results demonstrate that the low-temperature recovery approach is a promising approach for acid-free contamination recovery for PEM water electrolysis to promote stack reliability and durability.« less

The commercial viability of anion exchange membrane (AEM) electrolysis requires optimization of various stack components, with specific catalyst-ionomer combinations often yielding higher current densities, lowered Tafel slopes, and improved mass activity. In this joint theoretical-experimental study, theoretical calculations detail the impact of Versogen's piperidinium functional group on the complex, kinetically limiting oxygen evolution reaction, finding that the functional group can act as a promoter of specific steps (O*/O2* formation; H2O/O2 desorption with reaction enthalpies ranging between 0.2-0.6 eV at higher coverages of OxHy intermediates) on NiO and NiFeOx catalysts. In particular, Fe sites on the NiFeOx catalyst facilitate concerted mechanismsmore » of O*/O2* formation and H2O desorption with a low enthalpy of 0.5 eV; O2 desorption alone requires only 0.3 eV. In contrast, Versogen-IrO2 results in stronger Ir-O bonds, where the enthalpies for bond breaking (Ir-OH2 and Ir-O2) are considerably higher (1.4 eV and 1.6 eV, respectively). Rotating disk electrode studies utilized commercially available NiO and IrO2 and synthesized 7.5 wt % Fe in NiFeOx catalysts in combination with Versogen, a common AEM ionomer, and Nafion, an alternative binder. Electrochemical testing validated the impact of these mechanistic changes on ionomer-catalyst combinations, finding that Versogen particularly activates NiO and NiFeOx compared to IrO2. Following a 13.5 h hold at 1.8 V, mass activities and Tafel slopes improved to 34 +- 13 A g-1 and 79 +- 2 mV dec-1 (NiO) and 82 +- 4.9 A g-1 and 72 +- 2 mV dec-1 (NiFeOx). In contrast, Versogen-IrO2 only reached 17 +- 2.9 A g-1 and 81 +- 3 mV dec-1. Optimization of the ionomer-catalyst can yield significant increases in performance from initial activity and after an electrochemical conditioning procedure: this enhancement to the mass activity resulted in a 200.9 +- 106.1% improvement for Versogen-NiFeOx and 1284.2 +- 260.5% for Versogen-NiO. In contrast, Nafion-NiFeOx and -NiO offered moderate improvements of 39.1 +- 30.5% and 120.9 +- 59.1%, respectively.« less

Electrochemical carbon dioxide reduction (CO₂R) is a promising approach for the decentralized production of fuels such as ethylene (C₂H₄). However, the use of Cu, the most efficient metal CO₂R catalyst for the generation of C₂H₄ known to date, generally yields a product stream with poor selectivity. In an effort to increase selectivity, the reaction from CO₂ to C₂H₄ can be broken down into two steps using tandem CO₂R electrolyzers: formation of CO from CO₂ and subsequent reduction of CO to C₂H₄. Here, in this study, we present two novel tandem electrolyzer architectures that closely integrate two cathodes, one for COmore » generation and one for conversion to C₂H₄, while still enabling independent electrical control of the cathodic surfaces. Cathode segmentation in each of these designs also permits the controlled sequencing of mass flow of chemical intermediates in the order of Au to Cu cathode catalysts, in contrast to earlier work relying on uncontrolled, passive diffusion to facilitate the flow of chemical intermediates between catalysts. When comparing the performance of the newly developed electrolyzer cell designs with a dual electrolyzer system, we found that the dual electrolyzer system yields the highest C₂H₄ faradaic efficiencies (FEs) of 31% and C₂H₄ concentrations (∼8 mol %). However, a single Cu-containing electrolyzer outperformed all three tandem systems in terms of C₂H₄ FE (34%). Our findings, enabled by independent control of the two tandem cathode surfaces, indicate that tandem CO₂R systems need to be evaluated carefully by testing them at various relevant current densities.« less

This work investigates the use of roll-to-roll coating methods for the production of iridium oxide catalyst layers for proton exchange membrane water electrolyzers. Catalyst layers were produced using two coating methods: slot die and gravure. By varying the solids content of the catalyst ink and coating process variables loadings between 0.08 and 0.64 mg_Ir cm⁻² were prepared with relatively high spatial uniformity. However, at loadings below 0.2 mg_Ir cm⁻² microscopy reveals voids in the catalyst layer due to similar length scales of catalyst agglomerates and overall layer thickness. Electrochemical testing shows that these voids do not impact initial membrane electrodemore » assembly performance but lead to increased performance losses after potential cycling compared to spray coated catalyst layers.« less

Proton exchange membrane water electrolyzers rely on relatively expensive Ir-based catalysts for efficient and durable hydrogen production. To reduce system costs, Ir loadings can be reduced if performance and durability are maintained. Sputter deposition is a readily scalable method to synthesize uniform, low-loading catalyst layers with controlled composition. A catalyst applied directly to the porous transport layer can have advantages for performance, manufacturing simplicity, and catalyst recovery. Suitable porous transport layer porosity can minimize activity losses when reducing loadings. Here, methods are presented to deposit metallic Ir as well as amorphous and rutile Ir oxides. The activity and durability ofmore » these materials in the porous transport electrode architecture is evaluated. The metallic and amorphous forms have better initial activity, however, operation at 3 A cm⁻² with 0.1 mg Ir cm⁻² shows that only rutile IrO₂ maintains performance beyond 100 h with a 50 mV improvement after 700 h. A >10x reduced dissolution rate is shown for rutile IrO₂. With a low-porosity transport layer and 0.4 mg Ir cm⁻², a steady-state voltage decay rate of 6 µV h⁻¹ is achieved. The results demonstrate that sputter-deposited rutile IrO₂ porous transport electrodes with low Ir loading can be operated at high current density to reduce hydrogen production costs.« less

Despite many recent advances, overpotentials remain high for anion exchange membrane water electrolyzers (AEMWEs). Voltage breakdown analyses (VBA) can help decouple the origins of overpotentials and facilitate design decisions to improve cell performance, but studies investigating how to adapt and apply VBA to AEMWEs are lacking. Specifically, catalyst layer resistances and their contributions to overpotentials are not consistently quantified in water electrolysis and are rarely quantified for AEMWEs. This work presents a systematic methodology for VBA tailored to AEMWEs, including an approach to Tafel analysis in the absence of a reference electrode and under conditions where both the oxygen evolutionmore » reaction and hydrogen evolution reaction exhibit significant overpotentials. Catalyst layer resistance contributions are diagnosed via changes in the catalyst layer thickness, transport layer porosity, ionomer content, and electrolyte concentration. In this study, we explain discrepancies between inherent catalytic kinetics and device level performance and identify catalyst layer design strategies to reduce catalyst layer resistances.« less

This study investigates strategies to improve the quality of electrochemical impedance spectroscopy (EIS) measurements using reference electrodes (RE) in proton exchange membrane water electrolyzers (PEMWE). We demonstrate that adding a low impedance wire in parallel to the RE significantly enhances signal accuracy, especially at high frequencies. Additionally, we identify electrical pad heaters as a source of measurement noise. EIS measurements fulfilling Kramers–Kronig validity criteria were only achieved in their absence. These insights advance the diagnostic capabilities of REs in water electrolyzers and support more reliable, spatially resolved analysis of electrochemical losses within the cell.

Understanding water, evolved gas, and ionic transport in membrane-electrode-assemblies (MEAs) is essential for the development of high performance and durable anion exchange membrane water electrolyzers (AEMWEs). This study evaluates the MEA conditioning process, operating conditions, and short-term stability in a 1 M potassium hydroxide (KOH) electrolyte, focusing on the underlying transport phenomena. We observe a significant initial voltage loss in continuous cell operation, which could be associated with gas bubble accumulation, transport layer or flow field passivation, and changes in the catalyst oxidation state. Further, we investigate the effects of materials and operational configurations, including the membrane type and thickness,more » and the electrolyte flow rate, including KOH being fed to both electrodes as well as to the anode only. Furthermore, the effect of membrane drying temperature on ex situ as well as in situ electrochemical performance is evaluated. Finally, we discuss 700 h of AEMWE operation at 1 A/cm², highlighting the underlying degradation phenomena.« less