Recent Approaches for Cleaving the C─C Bond During Ethanol Electro‐Oxidation Reaction

Abstract

Direct ethanol fuel cells (DEFCs) play an indispensable role in the cyclic utilization of carbon resources due to its high volumetric energy density, high efficiency, and environmental benign character. However, owing to the chemically stable carbon‐carbon (C─C) bond of ethanol, its incomplete electrooxidation at the anode severely inhibits the energy and power density output of DEFCs. The efficiency of C─C bond cleaving on the state‐of‐the‐art Pt or Pd catalysts is reported as low as 7.5%. Recently, tremendous efforts are devoted to this field, and some effective strategies are put forward to facilitate the cleavage of the C─C bond. It is the right time to summarize the major breakthroughs in ethanol electrooxidation reaction. In this review, some optimization strategies including constructing core–shell nanostructure with alloying effect, doping other metal atoms in Pt and Pd catalysts, engineering composite catalyst with interface synergism, introducing cascade catalytic sites, and so on, are systematically summarized. In addition, the catalytic mechanism as well as the correlations between the catalyst structure and catalytic efficiency are further discussed. Finally, the prevailing limitations and feasible improvement directions for ethanol electrooxidation are proposed.

Platinum-Decorated Amorphous Sulfurized Palladium Nanowires for Effective Ethanol Oxidation Reaction

“…6 Nonetheless, the pricey Pt and Pd electrocatalysts display sluggish reaction kinetics for EOR, attributed to the high activation energy required for C−C bond cleavage (87.3 kcal•mol −1 ). 3 Generally, the EOR procedure involves two parallel and competing pathways, that are, the complete oxidation pathway (C1 pathway) with 12 electrons transfer and incomplete oxidation pathway (C2 pathway) with only 2 or 4 electrons transfer. 7,8 Nevertheless, the C1 selectivity of pure Pt and Pd electrocatalysts is demonstrated to be very low (<7.5%).…”

“…As a promising fuel choice for direct ethanol fuel cells (DEFCs), ethanol possesses a range of benefits, including environmental friendly, widespread, sustainable in source, nontoxic, and easy to store and transport. Most notably, its volumetric energy density is 6.28 kW h·L –1 significantly higher than that of methanol (4.05 kW h·L –1 ) and hydrogen (0.18 kW h·L –1 , at 20 MPa). − However, the lack of highly active and durable anodic electrocatalysts for ethanol oxidation reaction (EOR) is one of the significant challenges in this field. , To date, platinum (Pt) and palladium (Pd) remain the state-of-the-art anodic electrocatalysts in DEFCs . Nonetheless, the pricey Pt and Pd electrocatalysts display sluggish reaction kinetics for EOR, attributed to the high activation energy required for C–C bond cleavage (87.3 kcal·mol –1 ) .…”

“…Most notably, its volumetric energy density is 6.28 kW h·L –1 significantly higher than that of methanol (4.05 kW h·L –1 ) and hydrogen (0.18 kW h·L –1 , at 20 MPa). − However, the lack of highly active and durable anodic electrocatalysts for ethanol oxidation reaction (EOR) is one of the significant challenges in this field. , To date, platinum (Pt) and palladium (Pd) remain the state-of-the-art anodic electrocatalysts in DEFCs . Nonetheless, the pricey Pt and Pd electrocatalysts display sluggish reaction kinetics for EOR, attributed to the high activation energy required for C–C bond cleavage (87.3 kcal·mol –1 ) . Generally, the EOR procedure involves two parallel and competing pathways, that are, the complete oxidation pathway (C1 pathway) with 12 electrons transfer and incomplete oxidation pathway (C2 pathway) with only 2 or 4 electrons transfer. , Nevertheless, the C1 selectivity of pure Pt and Pd electrocatalysts is demonstrated to be very low (<7.5%). , Additionally, they are also susceptible to performance decay due to the poisoning effect of the *CO intermediate formed during the EOR C1 process.…”