The Application Of Nanoporous Gold Based Catalysts For The Direct Methanol Fuel Cell

As traditional fossil fuels become increasingly expensive and their use causes environmental pollution,it is urgent to find a more environmentally friendly and efficient energy conversion solution.The development of new power sources,represented by fuel cells,is one effective way to address this issue.Among them,direct methanol fuel cells have attracted attention due to their small size,portability,and high energy density.However,the commercial application of DMFC still faces certain obstacles,the most prominent of which is the slow kinetics of the anodic methanol oxidation and cathodic oxygen reduction reactions and the large amount of precious metal catalyst used,resulting in high costs.To reduce the amount of precious metal used in DMFC and improve the power density of the battery,common solutions include increasing the activity of the catalyst,optimizing the electrode catalytic layer structure,and selecting high-reactivity cathode oxidants.Nano-porous metal films produced by dealloying present excellent prospects for electrode applications due to their metal ligament/pore dual continuous structure.The continuous nano-scale metal ligaments provide high specific surface area as reaction sites,and can achieve rapid electron conductivity.The connected and adjustable pore structures provide a smooth channel for material transfer.The metal bonding between the active component and the metal carrier enhances the electrode structure stability.The above advantages have been confirmed in various types of fuel cells such as formic acid fuel cells,hydrogen-oxygen fuel cells,and hydrazine hydrate fuel cells.Based on this,this paper used nano-porous metal films as substrates to realize the macro-scale preparation technology of various types of NPG-based electrode materials,including NPG-Pt,NPG-Pd,and NPG-PtRu.The research focused on membrane electrode technology using the above electrode materials as the anode and cathode of DMFC,and achieved the following research results:（1）Large-scale preparation of NPG-PtRu and optimization of membrane electrode assembly（MEA）process for DMFC.With a self-designed electroplating device,high-loading（>0.3 mg/cm²）and uniform NPG-Pt₂Ru₁samples（>5 cm*5 cm）were prepared by controlling the pulse electroplating parameters,as well as the concentration and proportion of the plating solution.Electrochemical experiments showed that NPG-Pt₂Ru₁with a Pt loading of 0.2 mg/cm²exhibited the highest intrinsic activity and mass activity towards methanol electrooxidation reaction,with a Pt specific surface area of 62 m²/g.Moreover,NPG-Pt₂Ru₁showed excellent CO-tolerance with a CO oxidation onset potential of 0.55 V.NPG-Pt₂Ru₁was then used as the anode catalyst layer for DMFC,and the structure of the catalyst layer and gas diffusion layer were optimized.The results showed that the problem of mass transfer limitation at the anode disappeared when the NPG substrate pore size increased to 60nm,and the gas-liquid transport within the catalyst layer became smooth.The hydrophilic treatment of the gas diffusion layer also improved the mass transfer at the anode.Using NPG_60nm-Pt_200μgRu as the anode catalyst,a power density of 95 m W/cm²was achieved at 80℃,with Pt power efficiency and precious metal power efficiency being 10 and 3 times higher than those of the commercial catalyst PtRu/C.（2）NPG-based electrodes for H₂O₂reduction reaction at DMFC cathode.Firstly,the catalytic activity of NPG,NPG-Pt,and NPG-Pd towards H₂O₂reduction reaction was evaluated using a three-electrode system,and the effect of NPG pore size on the selectivity of H₂O₂reduction and H₂O₂self-decomposition reactions on the electrode surface was discussed.The experimental results showed that NPG with a pore size of15 nm and NPG-Pd with a pore size of 30 nm exhibited the most outstanding catalytic activity for H₂O₂reduction reaction,while the severe self-decomposition reaction of H₂O₂on the NPG-Pt surface led to the destruction of its structure.Secondly,the selected electrode materials were used for DMFC cathode,and the test results showed that the membrane electrode structure and hot-pressing process could solve the problem of NPG-Pt film fragmentation.NPG-Pt cathode exhibited the most outstanding DMFC performance,and the power density reached 110 m W/cm²at 80°C when the Pt loading was 80μg/cm².The voltage only decayed by 9%after continuous discharge at a current of 0.1 A/cm²for 5 hours,and its Pt power efficiency was about3 times that of DMFC cathode using O₂oxidant.In summary,this paper leverages the structural advantages of NPG-based thin film electrodes and optimizes the structure of the membrane catalytic layer and the type of oxidant to greatly reduce the amount of Pt catalyst while maintaining the DMFC power density.This provides a new direction for the development of low-cost and high-specific-energy DMFCs.