Selective Electrocatalysts Developed to Improve Direct Methanol Fuel Cell Performance

Researchers from the Institute of Process Engineering (IPE) of the Chinese Academy of Sciences recently have developed a new technology to increase performance of direct methanol fuel cells (DMFCs) using high-concentration methanol as fuel, thereby shedding some light on the design of clean and economical alternative energy sources for portable electric gadgets.

Fig. 1. DMFC assemblies. Schematic illustration showing a DMFC fabricated with selective electrocatalysts at the anode and cathode chambers. Inlet is the photograph of the assembled cell. (Image by YANG Jun)

When methanol, the fuel of DMFCs, crosses over from the anode to the cathode via the proton exchange membrane (PEM), fuel cell performance is considerably degraded, posing a big problem for the commercialization of DMFCs. Typically, Scientists use a variety of strategies to enhance DMFC performance at high concentrations of methanol. These include optimizing the fuel-feed system, modification of electrodes, membrane development and water management.

These conventional strategies do not fundamentally overcome the key obstacle, but inevitably complicate the design of DMFCs and hence increase their cost.

Yang Jun, an IPE Professor

Working with Feng Yan, a Doctoral Student, and Liu Hui, an Assistant Professor, Yang used selective electrocatalysts to operate a DMFC at methanol concentrations up to 15 M, a substitute technique for solving the methanol crossover in DMFCs.

The cathode and anode catalysts of DMFCs are generally based on platinum (Pt). These catalysts are not selective for the oxygen reduction reaction (ORR) at the cathode or the methanol oxidation reaction (MOR) at the anode. With a clear understanding of the mechanisms of electrode reactions in DMFCs, the Researchers designed and created noble metal-based heterogeneous electrocatalysts with superior catalytic activity and high selectivity for ORR and MOR.

Promisingly, the DMFCs worked very well with high-concentration methanol as fuel by adequately making use of the structural uniqueness and electronic coupling effects among the varied domains of the noble metal-based heterogeneous electrocatalysts.

As illustrated in Figure. 1, ternary Au-Ag2S-Pt nanocomposites with core-shell-shell structures exhibit greater anode selectivity because of the electronic coupling among their varied domains, while core-shell Au-Pd nanoparticles with thin Pd shells display superior cathode selectivity because of the synergistic effects between their thin Pd shell and Au core.

The as-fabricated DMFC with selective catalysts generates a maximum power density of 89.7 mW cm-2 at a methanol-feed concentration of 10 M, and maintains proper performance at methanol concentrations up to 15 M.

Next, we are going to optimize the overall size of the catalysts, e.g., using Au nanoclusters with fine diameters as starting materials to further enhance the activity/selectivity for DMFC reactions

Yang Jun, an IPE Professor

In this way, new technologies will be built to help enhance the design of more efficient and cost-effective DMFC systems.

The research received funding from the National Natural Science Foundation of China, and the Center for Mesoscience, IPE, CAS. Related research findings have been published in Science Advances in a paper titled, "A selective electrocatalyst-based direct methanol fuel cell operated at high concentration of methanol".

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