Ni–Fe phosphide deposited carbon felt as free-standing bifunctional catalyst electrode for urea electrolysis

A free-standing catalyst electrode for the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) in a urea electrolysis cell was synthesized by electroplating a Ni–Fe alloy onto carbon felt, followed by phosphidation (P-NiFe@CF). The prepared P-NiFe@CF catalyst consisted of Ni5P4, NiP2, and FeP with 3D flower-like P-NiFe architecture on CF. P-NiFe@CF exhibited excellent electrocatalytic activity for the UOR (demanding only 1.39 V (vs. RHE) to achieve 200 mA cm−2), and for the HER with a low overpotential of 0.023 V (vs. RHE) at 10 mA cm−2, indicating its feasibility as a bifunctional catalyst electrode for urea electrolysis. A urea electrolysis cell with P-NiFe@CF as both the free-standing anode and cathode generated a current density of 10 mA cm−2 at a cell potential of 1.37 V (vs. RHE), which is considerably lower than that of water electrolysis, and also lower than previously reported values. The results indicate that the P-NiFe@CF catalyst electrodes can be used as free-standing bifunctional electrodes for urea electrolyzers.

Enhanced Cell Performance and Improved Catalyst Utilization for a Direct Methanol Fuel Cell with an In-Plane Gradient Loading Catalyst Electrode

Direct methanol fuel cells (DMFCs) offer high energy density, simple liquid fuel storage, and the ability to operate at ambient temperature. They may be used in a variety of portable mobile power supplies, small civilian power supplies, and automotive power supplies. However, in the process of electrochemical reaction inside a DMFC, because the reactants and products are distributed unevenly, the in-plane concentration of reactants and reaction rate are different; thus, the current density generated in the active area shows a high degree of non-uniformity. The high local current density can easily lead to the acceleration of DMFC aging. As a result, the operating cost of the DMFC is increased and the service life is shortened, which limits the commercial application of DMFCs. In this work, we develop an in-plane gradient loading catalyst. The loading on both the anode and cathode catalysts was lower near the inlet and higher close to the outlet. The experimental results of the single-cell test show that the performance of the gradient loading catalyst electrode was enhanced by up to 19.8% compared with the uniform loading catalyst at 60 °C for the same catalyst loading, especially under high current densities. In addition, the catalyst utilization was improved for the gradient loading catalyst electrode. Hence, the proposed approach shows potential for reducing the cost and increasing the service life of DMFCs.

Ni-Fe phosphide deposited carbon felt as free-standing bifunctional catalyst electrode for urea electrolysis

A free-standing catalyst electrode for the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) in a urea electrolysis cell was synthesized by electroplating a Ni-Fe alloy onto carbon felt, followed by phosphidation (P-NiFe@CF). The prepared P-NiFe@CF catalyst consisted of Ni5P4, NiP2, and FeP with 3D flower-like P-NiFe architecture on CF. P-NiFe@CF exhibited excellent electrocatalytic activity for the UOR (demanding only 1.44 V (vs. RHE) to achieve 200 mA cm −2), and for the HER with a low overpotential of 0.065 V (vs. RHE) at 10 mA cm−2, indicating its feasibility as a bifunctional catalyst electrode for urea electrolysis. A urea electrolysis cell with P-NiFe@CF as both the free-standing anode and cathode generated a current density of 10 mA cm−2 at a cell potential of 1.42 V (vs. RHE), which is considerably lower than that of water electrolysis, and also lower than previously reported values. The results indicate that the P-NiFe@CF catalyst electrodes can be used as free-standing bifunctional electrodes for urea electrolyzers.

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.