Hollow Tungsten Carbide Prepared Using AMT as Enhanced Electrocatalyst for Hydrogen Evolution Reaction

Hydrogen energy is considered as the most promising renewable sources of energy to substitute fossil fuels. It has the advantages of zero-greenhouse emission, abundant resources, and high energy density. The electrocatalytic hydrogen evolution reaction (HER) using water splitting has received intense interest as an environmental-friendly technology consisting of HER and water oxidation reaction (WOR). Although the HER is a clean technology, it requires a high electric energy consumption and a high energetic efficiency. Thus, increasing the photocatalytic efficiency of HER is significantly necessary.

Platinum (Pt) is the most efficient metal catalysts possessing excellent catalytic performance to produced high cathodic current in the acidic electrochemical water splitting. However, the HER process has not reached a sufficient level due to the high cost and rarity of Pt catalysts. Tungsten carbide (WC) not only possesses platinum-like catalytic properties but wide pH operation range which presents potential use as low cost HER electrocatalysts.

Recently, hollow tungsten carbide has been prepared using ammonium metatungstate (AMT) as an enhanced electrocatalyst for hydrogen evolution reaction. The synthesis process of hollow tungsten carbide is as following procedures:

First, an aqueous solution with 10 wt% AMT was pumped into a Mini Spray Dryer B290 with air flow rate of 35 m3 h−1 and the solution feed rate of 10 ml min−1. The temperature for the drying air inlet was controlled at 473 K. The spray drying product was collected in a glass vessel. Then, the carburization process was conducted in a tube furnace by using CO as reducing agent and carbon source at high temperature. 10 g hollow AMT were put into a ceramic boat in the middle of a quartz tube in a tube furnace. Prior to the elevation of temperature, the quartz tube was firstly flushed by the gas mixture of CO/CO2 for 30 min in order to remove the air. Then the temperature was increased to 773 K with a rate of 5 °C min−1 and maintained at this temperature for 1 h. The flow rates of CO and CO2 were maintained at 200 and 20 mL min−1, respectively. After that, the temperature was again increased to 1023 K and maintained for 10 h to finalize the carbonization. The furnace was cooled down to room temperature in the atmosphere of CO/CO2 and the as-synthesized WC was obtained. For comparison, the bulk WC (B-WC) was synthesized as the same procedures while the precursor was the as-received pristine AMT but without the treatment by spray drying.

In conclusion, hollow tungsten carbide has been prepared using AMT as an enhanced electrocatalyst for hydrogen evolution reaction. The result revealed that the WC has a higher surface area and a larger pore volume than those for the bulky WC material, which offers it a highly efficient electrocatalytic structure for electrochemical reactions. In acid electrolyte, the hollow WC electrode could deliver a current density of −10 mA cm−2 for HER at an overpotential of 160 mV.

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