Uniting activity design principles of anode catalysts for direct liquid fuel cells†

Direct liquid fuel cells have advantages over hydrogen-based fuel cells and lithium-ion batteries for portable and mobile applications due to their high volumetric energy density and the convenient storage or refueling of liquid fuels. Unfortunately, the electrochemical oxidation of liquid fuels (such as methanol, ethanol, and formic acid) currently corresponds to ∼50% of the energy losses of these devices at operating conditions. Moreover, state-of-the-art catalysts for such critical reactions are generally composed of precious metals such as Pt and Pd, hindering the cost-effective implementation of these technologies. The development of novel catalyst design principles for electrochemical liquid fuel oxidation has been constrained by its complex, structure-sensitive reaction energetics that can involve multiple parallel, competitive reaction intermediates and pathways. In this review, we aim to dissect and bridge the understanding of fundamental energetics and the materials engineering of novel catalysts for the electrochemical oxidation of various liquid fuels. By deconvoluting these reactions into the energetics of different critical elementary steps, we define essential descriptors that govern the activity and selectivity of electrochemical liquid fuel oxidation. Several universal and fundamental design principles are proposed to optimize the catalytic performance of state-to-the-art and emerging electrocatalysts by tuning the chemistry and electronic structure of active sites. This review aims to provide a unique perspective connecting the electro-oxidation energetics of different liquid fuels with mechanistic and materials-centric studies to provide a holistic picture connecting the fundamental surface science with materials engineering for the rational design of electrocatalysts for liquid fuel oxidation.