The effect of surface morphology on electrocatalytic performances of Pt@Ni and Pt@Cr thin film catalysts for the methanol oxidation reaction

Direct methanol fuel cells (DMFCs) are attractive alternative energy sources due to their non-toxic nature, reduced hazardous pollutants, and high energy density. They can be used in a wide range of applications, among which the most significant include transportation and stationery and portable power sources. The main challenges for their widespread commercialization include the high cost of noble metal-based catalysts (mainly platinum), the poisoning of Pt catalysts by intermediates during methanol electrooxidation, issues with fuel crossover and long-term catalyst durability. Strategies to overcome these difficulties are directed towards alloying Pt with inexpensive and widely available metals through various deposition techniques and using innovative supports to improve Pt utilization. Surface morphology plays one of the key roles in improving the performance of electrocatalysts. Therefore, by precisely modifying surface structures at the atomic scale, the efficiency of catalysts can be significantly improved. Heat treatment is also efficient for promoting surface atom rearrangement, hence modifying the catalyst’s characteristics. This study investigated the influence of thermal annealing on the morphology and surface reconstruction of platinum electrodeposited Ni and Cr supports. The electrodeposition of Pt on Ni or Cr substrates was conducted under potentiostatic conditions in an H2PtCl6 solution. After the deposition, the as-prepared Pt@Ni and Pt@Cr electrodes were annealed in a reductive atmosphere (95% Ar + 5% H2) at 300 ◦C. The activity of the catalysts was tested for the methanol oxidation reaction. The influence of thermal treatment on the surface morphology was monitored using atomic force microscopy (AFM) focusing on surface morphology, roughness, and nanoscale structure. AFM revealed distinct surface features related to the Pt deposition process and thermal treatment, providing valuable insights into how these modifications influence catalytic behavior. It was found that even a modest annealing temperature of 300°C was enough to induce diffusion across the surface and grain boundary migrations that resulted in coalescence and particle growth. In addition to AFM, cyclic voltammetry and CO stripping techniques were used to evaluate the electrochemical activity. The annealed catalyst shows a notable improvement in methanol oxidation reaction performance, approximately 2.5 times greater than the as-prepared sample. Pt@Ni catalyst showed the best activity (considering the amount of precious metal consumed) reaching, at E~0.905 V, a mass-specific current density that is larger by one order of magnitude than that obtained on Pt@Cr catalysts. The observed behavior is attributed to the significant contribution of smaller Pt particles, the greater specific surface area, and the lack of agglomerates at the Pt@Ni electrode. Based on the obtained results it was pointed important role of surface characterization in understanding and optimizing the functional properties of catalysts for green energy.