Confinement Effects of Hollow Structured Pt-Rh Electrocatalysts toward Complete Ethanol Electrooxidation.

In the anodic ethanol oxidation reaction (EOR) for direct ethanol fuel cells, the coverage of hydroxide (OH) is a major adsorbent competing with C-C bond cleavage, which is necessary for complete ethanol oxidation (C1-pathway) and durability. Beyond utilizing a less-alkaline electrolyte that causes ohmic losses, an alternative strategy to optimize OH coverage is to intentionally exploit local pH changes near the electrocatalyst surface that are governed by a combination of released H during EOR and OH mass transport from the bulk solution. Here, we manipulate the local pH swing by fine-tuning the electrode porosity with PtRh hollow sphere electrocatalysts based on particle size (250 and 350 nm) and mass loading. With the smaller size of 250 nm, PtRh (∼50 μg cm) shows a high activity of 1629 A g (2488 A g) in a 0.5 M KOH-containing electrolyte, which is ∼50% higher than the most active binary catalysts to date. Moreover, a higher C1-pathway Faradaic efficiency (FE) of 38.3% and 80% longer durability are achieved with a 2-fold increase in mass loading. In the more porous electrodes, a local acidic environment created by hindered OH mass transport better optimizes OH coverage, providing more active sites for the desired C1-pathway and a continuous EOR.