New progress of alkaline membrane fuel cells by Chinese scientists

On October 27, 2022, Professor Gao Minrui of the University of Science and Technology of China and Professor Lansi of Nanjing University of Science and Technology published an article entitled “Nickel-molybdenum-niobium metallic glass for efficient hydrogen oxidation in hydroxide exchange membrane fuel” in the journal Nature Catalysis cells”.

By applying the amorphous metal glass structure catalyst to the anode hydrogen oxidation reaction of alkaline membrane fuel cells, the research team achieved a breakthrough in the catalytic activity and oxidation resistance of Ni-based catalysts, and achieved performance comparable to commercial platinum.

The co-corresponding authors of the paper are Gao Minrui and Lan Si; The co-first authors are Gao Feiyue, Liu Sinan, Ge Jiacheng, Zhang Xiaolong, and Zhu Li.

Due to the advantages of high specific energy and green pollution-free, hydrogen and oxygen fuel cells will play an important role in the world’s energy structure in the future. The dependence of proton exchange membrane fuel cells on platinum group catalysts has led to high system costs, and the emergence of alkaline membrane fuel cells has made it possible to use platinum-free metal electrocatalysts, and can reduce the cost of membranes, bipolar plates and other components in fuel cell systems, which is expected to gain market advantages in the future. However, at the anode hydrogen oxidation (HOR) end of the alkaline membrane fuel cell, the reaction kinetic rate of the catalyst is about two orders of magnitude lower than the acidic conditions, and the current stability window of Ni-based catalysts is less than 0.3 V, which is at risk of oxidative inactivation. Therefore, the design and creation of new anode catalysts with high activity and high oxidation resistance is a problem that needs to be solved in the practical application of alkaline membrane fuel cells.

Recently, Professor Gao Minrui’s team of University of Science and Technology of China and Professor Lansi team of Nanjing University of Science and Technology designed and developed a three-way nickel-molybdenum-niobium metal glass structure catalyst for the anodic hydroxidation reaction of alkaline membrane fuel cells, which greatly increased the oxidation resistance potential of nickel-based catalysts to a level similar to platinum of 0.8 V, and reached a catalytic activity comparable to platinum. The researchers designed a series of nickel-molybdenum-niobium catalysts of different components, and finally succeeded in preparing a series of amorphous metal glass structure catalysts due to the rapid cooling process of the melt spinning method that prevented the metal crystallization process (Figure 1). In the electrochemical analysis of different samples, it was found that the catalyst with metallic glass structure could exhibit an ultra-high oxidation resistance potential of 0.8 V, which was the optimal value of non-precious metal catalysts. Ni52Mo13Nb35 metallic glass has a catalytic activity comparable to Pt, which is currently the best performance among non-precious metal catalysts. Pt group catalysts on fuel cell anodes are generally prone to CO poisoning, because CO is preferentially adsorbed on the Pt surface, thus occupying the adsorption and dissociation site of hydrogen. The experimental results show that the Ni52Mo13Nb35 metal glass catalyst can still exhibit high HOR catalytic activity even with the addition of 2% CO gas to hydrogen fuel, while the Pt catalyst is completely inactivated (Figure 2).

Figure 1: Preparation and characterization of NiMoNb metallic glass strips.

Figure 2: Analysis and comparison of electrochemical activity of NiMoNb metallic glass strips of different components.

The results of the synchrotron radiation high-energy X-ray pair distribution function test show that the atomic-scale cluster connection mode provides an important guarantee for the stability and high activity of the amorphous structure. The point connection and line connection mode between the short program clusters make Ni52Mo13Nb35 metallic glass have higher reaction sites at the atomic scale, and molecular dynamics simulation and first-principles calculation results also show that Ni52Mo13Nb35 metallic glass has better intermediate adsorption energy (Figure 3).

Figure 3: Cluster connectivity comparison of NiMoNb metallic glass strips of different components and their effects on electrochemical activity.

The electrochemical stability test results show that the current attenuation of the Ni52Mo13Nb35 metallic glass catalyst after 18 hours of continuous operation at 0.8 V relative to RHE potential at room temperature is almost negligible. The catalyst also exhibits excellent stability at higher operating temperatures (45 °C). The results of ICP analysis showed that Ni52Mo13Nb35 metallic glass showed no obvious signs of electrochemical precipitation of Ni and Nb elements during HOR for more than 17 hours, and only a small amount of Mo elements were precipitated (< 5%). In contrast, crystalline Ni52Mo13Nb35 alloys exhibited a sharp loss of Mo elements (about 11%) after only 5 hours of stability testing. In situ Raman spectroscopy also showed that oxidized species were less likely to form on the surface of metallic glass structures than crystalline catalysts (Figure 4). The researchers speculate that during the synthesis of metallic glass, rapid cooling makes the metallic glass have good chemical homogeneity, and the lack of crystal defects that can easily cause local corrosion inside, both of which contribute greatly to the HOR stability of Ni52Mo13Nb35 metallic glass.

Fig. 4: Stability evaluation and spectroscopic mechanism study of Ni52Mo13Nb35 metallic glass.

The researchers used mechanical ball milling to make Ni52Mo13Nb35 metal glass strips into powder and test the performance in the fuel cell anode, and the optimized hydrogen and oxygen fuel cell obtained a current density of 338 mA cm-2 and a peak power density of 390 mW cm-2 at a voltage of 0.65 V. Hydrogen-to-air fuel cells also exhibit excellent performance, capable of delivering a current density of 201 mA cm-2 and a maximum power density of 253 mW cm-2 at 0.65 V.

Relevant research has been funded by the National Natural Science Foundation of China, the National Key R&D Program, and the Anhui Provincial Key Research and Development Program. (Source: Web of Science)

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