Ammonium Metatungstate Applied in Low-Cost Electrocatalyst for Hydrogen Evolution

Today, hydrogen is used in a variety of industrial applications. Initially, it was the basic material required in various chemical processes such as oil refining, the production of ammonia and methanol, and the synthesis of many polymers. In addition, hydrogen is also used in other industrial sectors, namely: glass and electronics production, metallurgy and food industry. Due to its characteristics, hydrogen is also considered to be one of the most important energy sources and can replace carbon-based fuels.

Platinum (Pt) is an expensive precious metal and its composite materials are still the most effective HER catalysts due to their superior catalytic activity. However, its high cost limits its applications. Reducing the loading of noble metal electrocatalysts with high activity and excellent stability for hydrogen evolution (HER) is still a focused challenge. The outstanding stability is attributed to metal particles-fixed in porous carbon structure. The Pt and WC nanoparticles loaded on the BMZ template (Pt-WC/BMZ) were prepared by a simple process. Ammonium metatungstate is applied in a low-cost electrocatalyst for hydrogen evolution, the produced catalyst shows high performance and excellent stability for hydrogen evolution. The Pt-WC-1,10/BMZ catalyst (the molar ratio of Zn/Co is 1:2) exhibits high performance and excellent stability for hydrogen evolution. The synthesis process of Pt-WC-/BMZ catalysts is as below:

First, the bimetallic Zn-Co-ZIFs (BMZ) are synthesized by typical solution precipitation. A solution of 0.326 g zinc nitrate hexahydrate and 0.620 g cobalt nitrate hexahydrate was ultrasonically dispersed into 10 mL of deionized water for 10 minutes to form a homogeneous solution. After that, the above solution was added to 10 mL of deionized water containing 1.024 g of 2-methylimidazole. The purple solution was incubated at room temperature for 24 hours, collected by centrifugation, washed with deionized water 5 times, and finally dried in a vacuum oven at 80°C overnight.

Then, 0.5 g of the prepared BMZ and 0.2 g of ammonium metatungstate hydrate were dissolved in 20 mL of chloroplatinic acid hexahydrate (3.86 mmol/L) and fully penetrated by ultrasonic dispersion for 10 minutes. The mixture was then incubated at room temperature for 10 hours, collected by centrifugation and dried in an oven at 80°C overnight. Finally, the product was calcined in a 5% H2/Ar atmosphere at 900°C at a heating rate of 5°C/min for 2.5 hours. By changing the mass ratio of chloroplatinic acid hexahydrate and ammonium metatungstate hydrate, Pt-WC-0.7,10/BMZ and Pt-WC-2.5,10/BMZ were synthesized in the same way. Pt/BMZ and WC/BMZ were prepared according to the standards of Pt-WC-1,10/BMZ without adding ammonium metatungstate hydrate and chloroplatinic acid hexahydrate, respectively.

In short, ammonium metatungstate is used in producing low-cost electrocatalysts for hydrogen evolution, and the produced catalyst exhibits high performance and excellent hydrogen evolution stability. The Pt and WC nanoparticles loaded on the BMZ template were prepared by a simple process. The Pt-WC-1,10/BMZ catalyst (the molar ratio of Zn/Co is 1:2) exhibits amazing activity in 0.5M H2SO4, with a low overpotential of 23mV at a current density of -10mVcm-2, a small Tafel slope of 40.1mV dec-1, and  long durability (the chronopotentiometric test is at least 3000 cycles and 8 hours).

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