Water Electrolysis Using a Porous IrO2/Ti/IrO2 Catalyst Electrode and Nafion Membranes at Elevated Temperatures

Porous IrO2/Ti/IrO2 catalyst electrodes were obtained by coating IrO2 on both sides of three types of porous Ti powder sheets (sample 1, sample 2, and sample 3) using different surface treatment methods, and a hydrogen evolution catalyst electrode was obtained by coating Pt/C on carbon gas diffusion layers. A Nafion115 membrane was used as an electrolyte for the membrane electrode assemblies (MEA). Water electrolysis was investigated at cell temperatures up to 150 °C, and the electrical characteristics of the three types of porous IrO2/Ti/IrO2 catalyst electrodes were investigated. The sheet resistance of sample 1 was higher than those of samples 2 and 3, although during water electrolysis, a high current density was observed due to the nanostructure of the IrO2 catalyst. In addition, the structural stabilities of Nafion and Aquivion membranes up to 150 °C were investigated by using small angle X-ray scattering (SAXS). The polymer structures of Nafion and Aquivion membranes were stable up to 80 °C, whereas the crystalline domains grew significantly above 120 °C. In other words, the initial polymer structure did not recover after the sample was heated above the glass transition temperature.

Heat-induced magnetic transition accelerates redox couple mediated electrocatalytic water oxidation in alkaline media

The redox couple oxidation as an initial step for oxygen evolution reaction (OER) may be key for high electricity consumption in electrochemical redox couple mediated water splitting. Here, we report a heat-induced magnetic transition strategy to speed up the oxidation kinetics of redox couples. The activation energy of Ni2+/Ni3+ redox couple oxidation was significantly decreased by heating the Ni0.5Fe0.5OxHy OER catalyst above Néel temperature (TN) of 70oC. In such a strategy, the heat in stead of electricity to overcome the spin flipping of Ni2+/Ni3+ oxidation through the heat-sensitive ferrimagnetic-to-paramagnetic spin state changes. The efficient heat-electricity coupling enables Ni0.5Fe0.5OxHy to produce the lowest OER overpotential of 170 mV at 100 mA cm-2 at 90 oC in alkaline electrolyte, outperforming the benchmark IrO2 catalyst. Our findings demonstrate the application potential of heat-sensitive magnetic materials in the field of electrocatalysis, which may inspire insights into designing of multi-energy complementary OER devices.

Unlocking the Potential of Single Atoms Loaded Geobacter Hybrid Catalyst as Bifunctional Electrocatalyst for Water Splitting

Single-atom metal (SA-M) catalysts with high dispersion of active metal sites allow maximum atomic utilization. However, conventional synthesis of SA-M catalysts involves high-temperature treatments, leading to a low yield with random distribution of atoms. Herein, a facile method to synthesize SA-M catalysts (M = Fe, Ir, Pt, Ru, Cu, or Pd) in a single step at ambient temperature, using the extracellular electron transfer capability of Geobacter sulfurreducens (GS), is presented. Interestingly, the SA-M is coordinated to three nitrogen (N) atoms adopting an MN3 on the surface of GS. Dry samples of SA-Ir@GS without further heat treatments show exceptionally high activity for OER when compared to benchmark IrO2 catalyst and comparable HER activity to commercial 10 wt.% Pt/C. The SA-Ir@GS electrocatalyst exhibits the best water‐splitting performance compared to other SA-M@GS, showing a low applied potential of 1.65 V to achieve 10 mA cm−2 in 1.0 M KOH solution with cycling over 5 h. The density functional calculations reveal that the large adsorption energy of H2O and moderate adsorption energies of reactants and reaction intermediates for SA-Ir@GS favorably improve its activity. This nature-based facile synthesis method of SA-M at room temperature provides a versatile platform for the preparation of other transition metal SA-M catalysts for various energy-related applications by merely altering the metal precursors. <br>

Unlocking the Potential of Single Atoms Loaded Geobacter Hybrid Catalyst as Bifunctional Electrocatalyst for Water Splitting

Single-atom metal (SA-M) catalysts with high dispersion of active metal sites allow maximum atomic utilization. However, conventional synthesis of SA-M catalysts involves high-temperature treatments, leading to a low yield with random distribution of atoms. Herein, a facile method to synthesize SA-M catalysts (M = Fe, Ir, Pt, Ru, Cu, or Pd) in a single step at ambient temperature, using the extracellular electron transfer capability of Geobacter sulfurreducens (GS), is presented. Interestingly, the SA-M is coordinated to three nitrogen (N) atoms adopting an MN3 on the surface of GS. Dry samples of SA-Ir@GS without further heat treatments show exceptionally high activity for OER when compared to benchmark IrO2 catalyst and comparable HER activity to commercial 10 wt.% Pt/C. The SA-Ir@GS electrocatalyst exhibits the best water‐splitting performance compared to other SA-M@GS, showing a low applied potential of 1.65 V to achieve 10 mA cm−2 in 1.0 M KOH solution with cycling over 5 h. The density functional calculations reveal that the large adsorption energy of H2O and moderate adsorption energies of reactants and reaction intermediates for SA-Ir@GS favorably improve its activity. This nature-based facile synthesis method of SA-M at room temperature provides a versatile platform for the preparation of other transition metal SA-M catalysts for various energy-related applications by merely altering the metal precursors. <br>

Nanoporous IrO2 catalyst with enhanced activity and durability for water oxidation owing to its micro/mesoporous structure

Micro/mesoporous IrO2 catalyst with an ultrahigh specific surface area of 363.3 m2 g−1 shows excellent electrocatalytic performance for the oxygen evolution reaction.