Iridium-Tungsten Oxide Composite Using APT as Precursor for Electrochemical Water Splitting

Hydrogen energy is a renewable clean energy that has been believed to be promising substitute to current energy source of fossil fuels. Electrochemical water splitting is a feasible approach to produce hydrogen gas in which hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) taking place at cathode and anode electrodes respectively.

Oxygen evolution reaction within the electrochemical reaction is the most important procedure in the energy production and storage devices due to high operating voltages, sluggish kinetics and high energy losses. Most of the OER catalysts are noble metal-based, such as Iridium (Ir), Ruthenium (Ru) based electrocatalysts. However, noble metals are quite expensive and has disadvantages.

In order to lower the expenses, tungsten trioxide (WO3) had been composited with the iridium dioxide (IrO2). The synthesis process of iridium-tungsten oxide (IrO2/WO3) composite using ammonium paratungstate (APT) as precursor for electrochemical water splitting is as below:

Ammonium Paratungstate (APT) with the molar concentration of 7.8 mmol lit−1 (20 ml) was used as a starting material for the preparation of pure tungsten oxide composite followed by the manufacturing of other mixed oxide composites. The PH of the APT precursor was adjusted to less than unity by adding few drops of hydrochloric acid (HCl, 36–38%). After that, the continuous stirring of the solution had been carried out for 60 min followed by the heating at 65 °C for 30 min to confirm the completion of the reaction. Then the resultant slurry was carried out under the filtration process followed by the washing with de-ionized water repeatedly again and again. Renate on the filter paper were placed in the oven at 50 °C for 6 h for drying. Dried product forming the hydrated tungsten tri-oxide i.e., was loaded in the furnace at 350 °C for 120 min in order to form the pure tungsten tri-oxide (WO3) as-synthesized composite.

The weight ratio of iridium and tungsten oxides is designed to 1:1. The calculated amounts of WO3 powder prepared by the above describe procedure were dissolved in the hexachloroiridium acid hydrated having concentration of 49.7 mmol L−1 (1 ml) followed by the addition of 5 ml absolute ethanol. Then, the resultant mixture was put in the oven at 65 °C for 120–180 min to remove the ethanol. In order to form the mixed oxide composites of iridium and tungsten oxides (IrO2/WO3), the dried product was calcined in the furnace for 240 min at 400 °C to ensure the crystal formation.

In summary, iridium-tungsten oxide (IrO2/WO3) composite using ammonium paratungstate (APT) as precursor for electrochemical water splitting had been produced successfully. Compared with IrO2, the iridium-tungsten oxide composite is twice the scale in catalytic activity, four-folds increase in bulk mass specific activity.

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