Galvanic replacement managing direct methanol fuel cells: AgPt nanotubes as a strategy for methanol crossover effect tolerance

The methanol crossover effect severely reduces the efficiency of direct methanol fuel cells once it affects the oxygen reduction reaction (ORR) that occurs in the cathode. Hence, methanol dilution has to be carried out to overcome this drawback. However, when methanol is employed as the fuel, its concentration is highly important to improve the performance of these electrochemical devices. Thus, although still very challenging, the rational design of efficient electrocatalysts for such systems via an ORR mechanism is vital. To this end, we reported the synthesis of AgPt nanotubes (1.0 wt% Pt) by a galvanic replacement approach using Ag nanowires as sacrificial templates, which were successfully immobilized on commercial silica. We demonstrated that such hollow AgPt-based material could be employed as a highly selective electrocatalyst, which promoted the system`s targeting for the ORR reaction, an essential pathway for renewable energy issues built on fuel cells. Our results were achieved in highly concentrated methanol solutions (up to 7.5 M), which was impossible with the commercial 20 wt% Pt on Vulcan XC-72R (E-TEK). Using theoretical calculations, we showed that Ag atoms were essential to avoid the poisoning as the reactions were less favorable to occur on its surface; then, the random configuration of AgPt nanotubes was crucial for the remarkable selectivity of the system, explaining the high performance of the electrocatalyst due to the synergistic effects between Ag and Pt in the AgPt/SiO2 electrocatalyst.