Electrocatalysis of formic acid on palladium and platinum surfaces: from fundamental mechanisms to fuel cell applications

Abstract

Formic acid as a natural biomass and a CO2 reduction product has attracted considerable interest in renewable energy exploitation, serving as both a promising candidate for chemical hydrogen storage material and a direct fuel for low temperature liquid fed fuel cells. In addition to its chemical dehydrogenation, formic acid oxidation (FAO) is a model reaction in the study of electrocatalysis of C1 molecules and the anode reaction in direct formic acid fuel cells (DFAFCs). Thanks to a deeper mechanistic understanding of FAO on Pt and Pd surfaces brought about by recent advances in the fundamental investigations, the "synthesis-by-design" concept has become a mainstream idea to attain high-performance Pt- and Pd-based nanocatalysts. As a result, a large number of efficient nanocatalysts have been obtained through different synthesis strategies by tailoring geometric and electronic structures of the two primary catalytic metals. In this paper, we provide a brief overview of recent progress in the mechanistic studies of FAO, the synthesis of novel Pd- and Pt-based nanocatalysts as well as their practical applications in DFAFCs with a focus on discussing studies significantly contributing to these areas in the past five years.

A mixed-solvent route to unique PtAuCu ternary nanotubes templated from Cu nanowires as efficient dual electrocatalysts

“…As shown in Figs 4a−c, the mass activities of Pt 27 Au 3 Cu-AA NTs are competitive (Table S4) at 0.95 V, which are respectively 7.3 and 3.4 times higher than that of commercial Pt/C. It means that the PtAuCu-AA NTs are efficient for both direct and indirect pathway [7]. Since the indirect pathway is considered to be a dehydration reaction resulted in a strong adsorption of CO * species [7], we mainly paid attention to the direct pathway.…”

“…It means that the PtAuCu-AA NTs are efficient for both direct and indirect pathway [7]. Since the indirect pathway is considered to be a dehydration reaction resulted in a strong adsorption of CO * species [7], we mainly paid attention to the direct pathway. Consequently, we studied the direct pathway stabilities of the catalysts by chronoamperometry at 0.43 V .…”

Electrocatalysts Prepared by Galvanic Replacement

“…These include Pt(Ag) and Pd(Ag) [232,241,244], PdAu and PtAu [237,238,245,246,252], PdPb [239], Pt(Bi) [124], Pd(Ni) [249] and Pd(Cu) [247,248] bimetallics as well as Pd(CuFe) [250] and Pt(PdFe) [253] trimetallic systems. The performance improvement of these systems is interpreted in terms of CO poison desorption from Pt in the presence of other metals (where the dehydration mechanism of FAO is operative [235]), and in terms of carbonaceous intermediates removal in the case of Pd (where the dehydrogenation mechanism prevails [235]). …”

“…Formic acid is recognized as a liquid fuel alternative to methanol since it is safer, it does not pose fuel cell membrane crossover problems, and has a higher oxidation potential, trailing only in volumetric energy density (see, for example, [234,235]). In a search of bimetallic or trimetallic catalysts that show improved activity for formic acid oxidation (FAO) with respect to the best electrode materials of Pd and Pt, galvanic replacement has been used as preparation route (see, for example, [126,[236][237][238][239][240][241][242][243][244][245][246][247][248][249][250][251][252][253]).…”

Synthesis and Electrocatalytical Application of Hybrid Pd/Metal Oxides/MWCNTs

“…DFAFC has a number of advantages over direct methanol fuel cells [1]: (i) it has higher power density and higher energy efficiency, (ii) crossover flux of formic acid through Nafion5 membrane is several times smaller than that of methanol [2], and (iii) formic acid is less toxic than methanol and does not have the risk of producing hazardous by-products during oxidation (e.g., formaldehyde). A number of reviews on DFAFC [1,[3][4][5][6][7][8] have been published.…”