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 test results, (f) Anti-methanol interference performance of the modified electrode

In recent years, with the global energy crisis and growing environmental concerns, there has been a significant shift toward sustainable energy solutions. This includes not only the storage but also the efficient conversion of renewable energy sources. Fuel cells and metal-air batteries are key technologies in this field, where the oxygen reduction reaction (ORR) at the cathode plays a crucial role in determining the overall performance, efficiency, and cost of these systems. Traditionally, platinum and its alloys have been the go-to catalysts for ORR due to their high activity and stability.

However, platinum is expensive and limited in supply, prompting researchers to explore alternative materials. Silver, although less costly than platinum, offers some catalytic activity and stability. Yet, its performance still lags behind that of platinum-based catalysts. The electrocatalytic behavior of a material is highly dependent on its nanostructure. Compared to zero-dimensional silver nanoparticles, one-dimensional silver nanowires (Ag NWs) show improved electrocatalytic performance, but they still fall short of expectations. One major limitation is their relatively low aspect ratio, which restricts their effectiveness in catalytic applications.

To address this, scientists have turned to two-dimensional silver nanonetworks (Ag NNs), which are formed by self-assembly of high-aspect-ratio silver wires. These structures offer better electrical and thermal conductivity, leading to enhanced catalytic performance and stability compared to lower-dimensional materials. Additionally, Ag NNs are less prone to aggregation, dissolution, or Ostwald ripening, making them promising candidates for next-generation ORR electrocatalysts.

To further enhance their performance, it is common to use carbon-based supports, such as graphene, which provide excellent electronic conductivity, large surface area, and good structural stability. Graphene, in particular, has emerged as an ideal support material due to its remarkable properties. However, current methods for preparing Ag NWs/GNSs nanocomposites often involve harsh conditions, making large-scale production challenging. Moreover, the low aspect ratio of many synthesized Ag NWs limits their ability to form effective Ag NNs.

In response to these challenges, a research team led by Zhang Guangjin from the Institute of Process Engineering, Chinese Academy of Sciences, successfully developed a scalable method to prepare two-dimensional Ag NN@POM-GNSs nanocomposites using polyoxometalates (POMs) as the sole reducing agent. This approach simultaneously reduces metal ions and graphite oxide, resulting in a highly efficient and stable ORR catalyst. Despite having a slightly more negative onset potential than commercial platinum, the material exhibits a higher limiting current density, superior stability, and excellent resistance to methanol interference. These advantages make it a strong candidate for replacing traditional platinum-based catalysts in fuel cell applications.

This groundbreaking research was supported by the National Natural Science Foundation of China (Grants 21071146 and 51002155) and the National High-Tech Research and Development Plan (863 Program, Grant 2012AA062903). The findings were published in the Journal of Materials Chemistry A (2013, 1, 11961–11969).

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