Process Engineering Preparation of High Activity Fuel Cell Oxygen Reduction Electrocatalyst

(a) Synthesis of Ag NN@POM-GNSs nanocomposites, (b) SEM images of the nanocomposites, (c) TEM images of the nanocomposites, (d) ORR linear sweep voltammetry comparison, (e) Stability evaluation, (f) Anti-methanol interference performance of Ag NN@POM-GNSs modified electrodes

In recent years, with the growing global energy crisis and increasing environmental concerns, there has been a rising focus on sustainable energy solutions, including energy storage and conversion technologies. Fuel cells and metal-air batteries are key players in this field, and their performance is heavily dependent on the efficiency of oxygen reduction reactions (ORR) at the cathode. Platinum-based catalysts have long been the standard for ORR due to their high activity and stability. However, their high cost and limited availability have driven researchers to explore alternative materials.

Silver, being the most affordable precious metal, offers some catalytic activity and stability—only about 2% of that of platinum—but its performance still lags behind. This gap in performance is partly attributed to the structure of the nanomaterials used. Compared to zero-dimensional silver nanoparticles, one-dimensional silver nanowires (Ag NWs) show better electrocatalytic properties, yet they still fall short of expectations. One major limitation is the low aspect ratio of Ag NWs, which limits their effectiveness.

To address these challenges, scientists have turned to two-dimensional silver nano-networks (Ag NN), which are formed by self-assembly of high-aspect-ratio silver wires. These structures offer improved conductivity, thermal stability, and resistance to aggregation, making them promising candidates for ORR electrocatalysts. Additionally, when combined with suitable support materials like graphene, their performance can be further enhanced.

Graphene, known for its excellent electronic conductivity, large surface area, and chemical stability, has become an ideal support for catalysts. However, traditional methods of preparing Ag NWs/GNSs composites often involve harsh conditions and low aspect ratios, making it difficult to achieve large-scale production or form effective Ag NN structures.

A breakthrough was recently achieved by Zhang Guangjin's research team at the Institute of Process Engineering, Chinese Academy of Sciences. They successfully synthesized Ag NN@POM-GNSs nanocomposites on a large scale using polyoxometalates (POMs) as the sole reducing agent. This method not only reduced metal ions but also simultaneously reduced graphite oxide, leading to a highly efficient and stable catalyst. The resulting material showed superior ORR performance compared to conventional silver-based catalysts, with a higher current density and better stability, despite having a slightly lower onset potential than commercial platinum. It also exhibited strong resistance to methanol interference, making it a viable candidate for replacing platinum-based catalysts in fuel cells.

This study was supported by the National Natural Science Foundation of China (Grant No. 21071146, 51002155) and the National High-Tech Research and Development Plan (863 Program, Grant No. 2012AA062903). The findings were published in the Journal of Materials Chemistry A (2013, 1, 11961–11969).

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