Abstract
The ethanol oxidation reaction (EOR) has drawn increasing interest in electrocatalysis and fuel cells by considering that ethanol as a biomass fuel has advantages of low toxicity, renewability, and a high theoretical energy density compared to methanol. Since EOR is a complex multiple-electron process involving various intermediates and products, the mechanistic investigation as well as the rational design of electrocatalysts are challenging yet essential for the desired complete oxidation to CO2. This mini review is aimed at presenting an overview of the advances in the study of reaction mechanisms and electrocatalytic materials for EOR over the past two decades with a focus on Pt- and Pd-based catalysts. We start with discussion on the mechanistic understanding of EOR on Pt and Pd surfaces using selected publications as examples. Consensuses from the mechanistic studies are that sufficient active surface sites to facilitate the cleavage of the C–C bond and the adsorption of water or its residue are critical for obtaining a higher electro-oxidation activity. We then show how this understanding has been applied to achieve improved performance on various Pt- and Pd-based catalysts through optimizing electronic and bifunctional effects, as well as by tuning their surface composition and structure. Finally we point out the remaining key problems in the development of anode electrocatalysts for EOR.
Highlights
Rising demands for energy coupled with concerns over ecosystem damage and growing consumption of non-regenerative fossil energy pose a great need for clean and efficient power sources [1,2,3,4]
C1 pathway always involves the participation of water or its adsorption residue, a good electrocatalyst must be able to activate both ethanol and water adsorption, which can be achieved by varying the composition and structure of the rationally designed catalysts
We found that the enhancement of electrocatalytic activity does not originate from the increase of active surface area, but is due to the variation of relative contributions of the two pathways as evidenced by in situ infrared spectroscopic results shown in Figure 13 [24]
Summary
Rising demands for energy coupled with concerns over ecosystem damage and growing consumption of non-regenerative fossil energy pose a great need for clean and efficient power sources [1,2,3,4]. Ethanol which can be produced on a massive scale from biomass feed stocks originating from agriculture (first-generation bioethanol), forestry, and urban residues (second-generation bioethanol), is attracting increasing interest [5,6,7,8]. The relatively sluggish kinetics for the ethanol oxidation reaction (EOR) presents a major roadblock for the development of direct ethanol fuel cells (DEFCs) [3,7]. Selectively enhancing the C1 pathway by rational design of high performance catalysts is an effective way to increase the DEFC efficiency. To rationally design Pt- or Pd-based materials as anode catalysts and to develop DEFC technology, a better understanding of the structure-electrocatalytic activity relationships in the EOR is a pre-requisite. Selected examples are only used to facilitate the discussion and inevitably we may have omitted other significant contributions in the field
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