Tae-Ho Kim

Tungsten oxides (WO _x ) are promising supports for Platinum (Pt) catalysts in the hydrogen evolution reaction (HER). However, how changes to the WO _x state and phase influence Pt active site characteristics and why these factors affect the HER performance are still not clearly understood. In this study, Pt catalysts were synthesized on WO ₃ and WO _2+x supports with identical Pt loading to identify the effect on HER performance according to different WO _x support phases. Pt existed as surface particles on WO ₃ whereas it was likely present in an atomic‐scale form on the sub‐surface region in WO _2+x . This difference in structure changed the availability of active sites and the electronic structure of Pt. It also led to different HER behavior depending on the electrolyte environment. The synthesized Pt/WO ₃ and Pt/WO _2+x catalysts exhibited significant differences under alkaline conditions. In particular, the Pt/WO ₃ catalyst showed roughly three times higher mass activity and 33 times higher specific activity than commercial Pt/C (Tanaka). However, the difference between Pt/WO ₃ and Pt/WO _2+x had little effect on the HER performance under acidic conditions. This study provides scientific insights into how Pt catalyst design with different WO _x phases influences electrochemical HER characteristics.

Hydrogen production via anion exchange membrane water electrolysis (AEMWE) offers a cost-effective pathway to green hydrogen by enabling the use of earth-abundant OER catalysts and low-cost hardware. However, the cathodic hydrogen evolution reaction (HER) remains a key limitation because alkaline HER on Pt is hindered by sluggish water-activation kinetics, requiring higher Pt loadings than those used in acidic systems. Here, we report a cobalt fluoride–modified Pt catalyst supported on Vulcan carbon (Pt/CoF2@VC) as a low-Pt alkaline HER cathode. By comparing CoF2- and CoOx-modified supports at matched Co content, we show that the optimized CoF2-derived support promotes strong spatial and electronic coupling between Pt nanoparticles and Co-containing domains. Post-activation XPS reveals a pronounced loss of surface Co–F signatures and the emergence of Co(oxy)hydroxide-like surface features, suggesting substantial surface reconstruction of the CoF2-derived domains. This interfacial environment is correlated with earlier CO oxidation onset, lower charge-transfer resistance, and enhanced alkaline HER activity. The optimized Pt/CoF2@VC-1 catalyst delivers an overpotential of 128.5 mV at 50 mA cm-2 and a fivefold higher Pt mass activity than commercial Pt/C. When applied as a low-Pt cathode in AEMWE, Pt/CoF2@VC-1 achieves 1.813 V at 3.0 A cm⁻² with a Pt loading of 0.10 mgPt cm-2, outperforming a Pt/C cathode under identical conditions. These results highlight fluoride-derived Pt–Co interfacial engineering as a promising strategy for improving low-Pt AEMWE cathodes.

Understanding of how interactions between the support materials and Pt electrocatalysts affect electrocatalytic activity behavior is crucial for designing efficient hydrogen evolution reaction (HER) electrocatalysts in alkaline media. In this study, we systematically investigate Pt nanoparticles supported on La-based perovskites with different B-site metals (LaMO₃, M = Ni, Co, and Fe) to elucidate the correlation between the support properties and the electrocatalytic activity of Pt. Modulating the B-site metal in LaMO₃ governs the surface reducibility of the support, which regulates the oxygen vacancy concentration of perovskite supports and the d-band center of the supported Pt. This, in turn, significantly affects H₂O dissociation kinetics and hydrogen adsorption behavior. Among the series, Pt supported on the LaNiO₃ exhibited the highest alkaline HER activity, characterized by a near-zero water dissociation barrier (0.01 eV) and the most optimally tuned hydrogen adsorption energy (-0.08 eV). These findings demonstrate that tailoring the electronic structure and surface properties of perovskite supports is an effective strategy for optimizing Pt-support interactions and advancing the design of high-performance Pt-based electrocatalysts for alkaline HER electrocatalysts.

Anion exchange membrane water electrolysis is an emerging technology for cost-effective hydrogen production, but its practical deployment is limited by inefficient electrode architectures that suffer from poor mass transport, inadequate interfacial contact within the assembled cell, and insufficient reliability. Here we show a high-performance and durable oxygen evolution electrode, a NiFe-based functionalized porous transport layer (NiFe-f-PTL), that integrates catalytic activity and porous transport functionality into a single structure with interfacial compatibility. Fabricated via a simple tape-casting process, this architecture minimizes interfacial resistance and enhances mass transport, resulting in a high current density of 6.73 A cm^-2 at 1.8 V_cell under steady-state operation. It further demonstrates over 2142 hours of stable operation, maintaining structural integrity and catalytic activity. These results highlight the importance of electrode architecture at the membrane electrode assembly level and provide a scalable strategy for developing reliable and high-performance anion exchange membrane water electrolysis systems.

While unitized regenerative fuel cells (URFCs) are promising for renewable energy storage, their efficient operation requires simultaneous water management and gas transport, which is challenging from the standpoint of water management. Herein, a novel approach is introduced for examining the alignment hydrophilic pattern of a Ti porous transport layer (PTL) with the flow field of a bipolar plate (BP). UV/ozone patterning and is employed to impart amphiphilic characteristics to the hydrophobic silanized Ti PTL, enabling low-cost and scalable fabrication. The hydrophilic pattern and its alignment with the BP are comprehensively analyzed using electrochemical methods and computational simulations. Notably, the serpentine-patterned (SP) Ti PTL, wherein the hydrophilic channel is directly aligned with the serpentine flow field of the BP, effectively enhances oxygen removal in the water electrolyzer (WE) mode and mitigates water flooding in the fuel cell (FC) mode, ensuring uninterrupted water and gas flow. Further, URFCs with SP configuration exhibit remarkable performance in the WE and FC modes, achieving a significantly improved round-trip efficiency of 25.7% at 2 A cm⁻².

Anion-exchange membrane water electrolysis is a promising technology for economical green hydrogen production; however, the corresponding industrial applications are limited by the lack of reliable polymer electrolytes. To address this problem, we developed chain-extender-derived high-molecular-weight hexyltrimethylammonium-tethered polycarbazoles (HQPC-TMA-x's) with compelling membrane characteristics, including high ionic conductivity, mechanical robustness, and high alkaline stability. Owing to its polycarbazole backbone, HQPC-TMA-x alleviated the problems due to ionomer adsorption on the electrode. In the single-cell configuration, the best-performing polymer (HQPC-TMA-2.4) achieved an unprecedented current density of 14.6 A cm⁻² at 2.0 V with a Ni–Fe alloy anode and low-cost cell hardware, additionally showing superior pure-water-electrolysis and direct-seawater-electrolysis performances. HQPC-TMA-2.4 exhibited in situ durability at a high current density of 1.0 A cm⁻² for 1000 h with low irreversible degradation rates of 52 and 6 μV h⁻¹ for platinum group metal (PGM) and PGM-free cells, respectively, demonstrating the reliability of this polymer in practical settings.

In vanadium redox flow batteries (VRFBs), simultaneously achieving high proton conductivity, low vanadium-ion permeability, and outstanding chemical stability using electrolyte membranes is a significant challenge. In this study, we report the fabrication of a tri-directional poly(2,5-benzimidazole) (T-ABPBI) membrane using a direct casting method. The direct-cast T-ABPBI (D-T-ABPBI) membrane was fabricated by modifying the microstructure of the membrane while retaining the chemical structure of ABPBI, having outstanding chemical stability. The D-T-ABPBI membrane exhibited lower crystallinity and an expanded free volume compared to the general solvent-cast T-ABPBI (S-T-ABPBI) membrane, resulting in enhanced hydrophilic absorption capabilities. Compared to the S-T-ABPBI membrane, the enhanced hydrophilic absorption capability of the D-T-ABPBI membrane resulted in a decrease in the specific resistance (the area-specific resistance of S-T-ABPBI and D-T-ABPBI membrane is 1.75 and 0.98 Ωcm², respectively). Additionally, the D-T-ABPBI membrane showed lower vanadium permeability (3.40 × 10⁻⁷ cm² min⁻¹) compared to that of Nafion 115 (5.20 × 10⁻⁷ cm² min⁻¹) due to the Donnan exclusion effect. Owing to the synergistic effects of these properties, the VRFB assembled with D-T-ABPBI membrane had higher or equivalent coulomb efficiencies (>97%) and energy efficiencies (70–91%) than Nafion 115 at various current densities (200–40 mA cm⁻²). Furthermore, the D-T-ABPBI membrane exhibited stable performance for over 300 cycles at 100 mA cm⁻², suggesting its outstanding chemical stability against the highly oxidizing VO₂⁺ ions during practical VRFB operation. These results indicate that the newly fabricated D-T-ABPBI membranes are promising candidates for VRFB application.

A new hydrocarbon-based (HC) composite membrane was developed using liquid crystal polymer (LCP)-nonwoven fabrics for application in proton exchange membrane water electrolysis (PEMWE). A copolymer of sulfonated poly(arylene ether sulfone) with a sulfonation degree of 50 mol% (SPAES50) was utilized as an ionomer for the HC membranes and impregnated into the LCP-nonwoven fabrics without any surface treatment of the LCP. The physical interlocking structure between the SPAES50 and LCP-nonwoven fabrics was investigated, validating the outstanding mechanical properties and dimensional stability of the composite membrane in comparison to the pristine membrane. In addition, the through-plane proton conductivity of the composite membrane at 80 °C was only 15% lower than that of the pristine membrane because of the defect-free impregnation state, minimizing the decrease in the proton conductivity caused by the non-proton conductive LCP. During the electrochemical evaluation, the superior cell performance of the composite membrane was evident, with a current density of 5.41 A/cm² at 1.9 V, compared to 4.65 A/cm² for the pristine membrane, which can be attributed to the smaller membrane resistance of the composite membrane. From the results of the degradation rates, the prepared composite membrane also showed enhanced cell efficiency and durability during the PEMWE operations.

Block copolymers generally have peculiar morphological characteristics, such as strong phase separation. They have been actively applied to polymer electrolyte membranes for proton exchange membrane fuel cells (PEMFCs) to obtain well-defined hydrophilic regions and water channels as a proton pathway. Although molecular simulation tools are advantageous to investigate the mechanism of water channel formation based on the chemical structure and property relationships, classical molecular dynamics simulation has limitations regarding the model size and time scale, and these issues need to be addressed. In this study, we investigated the morphology of sulfonated block copolymers synthesized for PEM applications using a mesoscale simulation based on the dynamic mean-field density functional method, widely applied to investigate macroscopic systems such as polymer blends, micelles, and multi-block/grafting copolymers. Despite the similar solubility parameters of the monomers in our block-copolymer models, very different morphologies in our 3D mesoscale models were obtained. The model with sulfonated monomers, in which the number of sulfonic acid groups is twice that of the other model, showed better phase separation and water channel formation, despite the short length of its hydrophilic block. In conclusion, this unexpected behavior indicates that the role of water molecules is important in making PEM mesoscale models well-equilibrated in the mesoscale simulation, which results in the strong phase separation between hydrophilic and hydrophobic regions and the ensuing well-defined water channel. PEM synthesis supports the conclusion that using the sulfonated monomers with a high sulfonation degree (32.5 mS/cm) will be more effective than using the long hydrophilic block with a low sulfonation degree (25.2 mS/cm).