Research progress of Pt-based electrocatalysts for hydrogen fuel cells with high toxicity resistance

<p indent="0mm">The gradual depletion of fossil energy sources and the excessive emission of greenhouse gases have significantly contributed to global warming, profoundly impacting the natural environment. Proton exchange membrane fuel cells (PEMFCs), specifically hydrogen (H₂) fuel cells, offer a promising solution by converting chemical energy directly into electrical energy through electrochemical reactions. PEMFCs boast numerous advantages, including zero emissions, high power density, rapid response times, and a simple structure, effectively mitigating the effects of the energy crisis and environmental degradation. Based on their operating temperatures, PEMFCs are categorized into low-temperature PEMFCs (LT-PEMFCs) and high-temperature PEMFCs (HT-PEMFCs). In LT-PEMFCs, operating at lower temperatures in the presence of water, water serves as the proton transport medium. Conversely, in HT-PEMFCs, proton conductivity relies on a different mechanism. Nafion, which is highly dependent on a hydrated condition, exhibits a dramatic drop in conductivity when the operating temperature exceeds 100°C. Polybenzimidazole (PBI) membranes, known for their excellent thermal and chemical stability, have garnered significant attention for high-temperature PEM applications, providing better proton conductivity under anhydrous conditions. However, large-scale hydrogen production technologies often fail to meet purity requirements due to high associated costs, with less than 5% of the globally produced H₂ coming from electrolytic water. For instance, most available H₂ is derived from methane steam reforming, introducing gaseous impurities such as carbon monoxide (CO), sulfuretted hydrogen (H₂S), and ammonia (NH₃) when used as fuel. These impurities can significantly degrade the performance of the electrode catalyst. The presence of trace amounts of CO in H₂ fuel poisons the catalyst during the reaction process. When reformate H₂ is supplied in a PEMFC, these concentrations CO can cause CO-poisoning and activity degradation. For the commercial Pt anodes, it is noted that the acknowledged maximum CO poisoning limits are 10 and <sc>100 ppm,</sc> respectively. A typical method for overcoming CO poisoning is the further purification of the hydrogen fuel after the reforming process, which can minimize the CO concentration. However, even for the CO concentration limits to <sc>0.2 ppm,</sc> the efficiency of PEMFCs is considerably reduced. Furthermore, the purification cycles required to achieve such low CO concentrations prohibitively increase the costs. Additionally, the release of phosphoric acid (PA) during HT-PEMFC operation can lead to phosphoric acid poisoning, reducing catalyst activity. The catalysts used in PEMFCs, primarily based on precious metals like platinum (Pt), exhibit superior electrocatalytic properties but are susceptible to toxicity and have limited stability. Pt, with its unique d-band structure of 5d electron orbitals, is the most efficient electrocatalysts for PEMFCs. The hydrogen oxidation reaction (HOR) rate on Pt-based nanoparticles is very fast, allowing the Pt load of the anode catalyst to be as low as <sc>0.05 mg cm⁻².</sc> However, the oxygen reduction reaction (ORR) at the cathode is about five orders of magnitude slower than the HOR at the anode, requiring a higher Pt load <sc>(~0.4 mg cm⁻²)</sc> to maintain performance. While Pt-based catalysts are highly efficient for the HOR at the anode, their significantly slower kinetics during the ORR at the cathode require increased Pt loadings. This discrepancy contributes to reduced catalyst stability and higher costs, thereby hindering widespread commercial adoption. Therefore, it is imperative to design and improve Pt-based catalysts to enhance the utilization rate and anti-poisoning ability of Pt. This paper reviews the current application status of Pt-based catalysts. It begins by describing the toxicity challenges faced by PEMFCs, focusing on the design of Pt-based catalysts to improve anti-toxicity. Finally, the development direction of Pt-based catalysts in PEMFCs is discussed and prospected.