Potential-Dependent Ionomer Rearrangement on the Pt Surface in Polymer Electrolyte Membrane Fuel Cells

The interface between the catalyst and the ionomer in the catalyst layer of polymer electrolyte membrane fuel cells (PEMFCs) has been a subject of keen interest, but its effect on durability has not been fully understood due to the complexity of the catalyst layer structure. Herein, we utilize a Pt nanoparticle (NP) array electrode fabricated using a block copolymer template as the platform for a focused investigation of the interfacial change between the Nafion thin film and the Pt NP under a constant potential. A set of analyses for the electrodes treated with various potentials reveals that the Nafion thin film becomes densely packed at the intermediate potentials (0.4 and 0.7 V), indicating an increased ionomer–catalyst interaction due to the positive charges formed at the Pt surface at these potentials. Even for a practical PEMFC single cell, we demonstrate that the potential holding at the intermediate potentials increases ionomer adsorption to the Pt surface and the oxygen transport resistance, negatively impacting its power performance. This work provides fresh insight into the mechanism behind the performance fade in PEMFCs caused by potential-dependent ionomer rearrangement

Electroconductive Polythiophene Nanocomposite Fibrous Scaffolds for Enhanced Osteogenic Differentiation via Electrical Stimulation

Biophysical cues are key distinguishing characteristics that influence tissue development and regeneration, and significant efforts have been made to alter the cellular behavior by means of cell–substrate interactions and external stimuli. Electrically conductive nanofibers are capable of treating bone defects since they closely mimic the fibrillar architecture of the bone matrix and deliver the endogenous and exogenous electric fields required to direct cell activities. Nevertheless, previous studies on conductive polymer-based scaffolds have been limited to polypyrrole, polyaniline, and poly­(3,4-ethylenedioxythiophene) (PEDOT). In the present study, chemically synthesized polythiophene nanoparticles (PTh NPs) are incorporated into polycaprolactone (PCL) nanofibers, and subsequent changes in physicochemical, mechanical, and electrical properties are observed in a concentration-dependent manner. In murine preosteoblasts (MC3T3-E1), we examine how substrate properties modified by adding PTh NPs contribute to changes in the cellular behavior, including viability, proliferation, differentiation, and mineralization. Additionally, we determine that external electrical stimulation (ES) mediated by PTh NPs positively affects such osteogenic responses. Together, our results provide insights into polythiophene’s potential as an electroconductive composite scaffold material

Anode Reinforcement by Polydopamine Glue in Anion Exchange Membrane Water Electrolysis

Durable catalyst layers (CLs) are essential for the commercialization of anion exchange membrane water electrolyzers (AEMWEs). However, the insufficient binding strengths of typical anion exchange ionomers often lead to CL disintegration and detachment from porous transport layers, resulting in rapid performance deterioration during the early stage of operation. Herein, coating the anode CL with polydopamine (PDA) is proposed as a solution to this problem; the coating enhances the mechanical integrity of the anode CL and its interfacial adhesion to the porous transport layer through electronic interactions. Furthermore, the aerophobic property of PDA helps remove O2 bubbles from the catalyst surface to improve the AEMWE performance. An AEMWE with the PDA coating exhibits stable operation for 300 h without any sign of initial degradation while maintaining high energy efficiency (>91.6%, higher heating value), underscoring the importance of the mechanical robustness and interfacial adhesion of the anode CL for achieving high-durability AEMWEs

Reduction of Transition-Metal Columbite-Tantalite as a Highly Efficient Electrocatalyst for Water Splitting

We successfully report a liquid–liquid chemical reduction and hydrothermal synthesis of a highly stable columbite-tantalite electrocatalyst with remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance in acidic media. The reduced Fe0.79Mn0.21Nb0.16Ta0.84O6 (CTr) electrocatalyst shows a low overpotential of 84.23 mV at 10 mA cm–2 and 103.7 achieved at 20 mA cm–2 current density in situ for the HER and OER, respectively. The electrocatalyst also exhibited low Tafel slopes of 104.97 mV/dec for the HER and 57.67 mV/dec for the OER, verifying their rapid catalytic kinetics. The electrolyzer maintained a cell voltage of 1.5 V and potential–time stability close to that of Pt/C and RuO2. Complementary first-principles density functional theory calculations identify the Mn sites as most active sites on the Fe0.75Mn0.25Ta1.875Nb0.125O6 (100) surface, predicting a moderate Gibbs free energy of hydrogen adsorption (ΔGH* ≈ 0.08 eV) and a low overpotential of η = 0.47 V. The |ΔGMnH*| = 0.08 eV on the Fe0.75Mn0.25Ta1.875Nb0.125O6 (100) surface is similar to that of the well-known and highly efficient Pt catalyst (|ΔGPtH*| ≈ 0.09 eV)

Contact Problems of IrO_<i>x</i> Anodes in Polymer Electrolyte Membrane Water Electrolysis

Green-hydrogen production by polymer electrolyte membrane water electrolysis (PEMWE) is limited by the use of expensive Ir-based catalysts, presenting a key challenge in achieving a low-IrOx-loaded membrane electrode assembly (MEA). Here, we investigate the abnormally poor performance and large high-frequency impedances in the ultralow-IrOx-loaded MEA (as low as 0.07 mg cm–2) for PEMWE. We reveal that these primarily originate from the electron transport problem in the native oxide on the Ti porous transport layer (PTL). Based on the metal–insulator band model, we conclude that the upward band bending by the Schottky contact with the high-work-function IrOx and the pinch-off effect by massive ionomer contact are the major causes of electron conductivity loss of the Ti oxide. This study highlights the importance of the catalyst/PTL interface and reveals that modulation of the catalyst work function and ionomer distribution is necessary to achieve high-performing but cheap water electrolysis