Tailored Electron Transfer Pathways in Au_core/Pt_shell–Graphene Nanocatalysts for Fuel Cells

Abstract

Aucore/Ptshell–graphene catalysts (G‐Cys‐Au@Pt) are prepared through chemical and surface chemical reactions. Au–Pt core–shell nanoparticles (Au@Pt NPs) covalently immobilized on graphene (G) are efficient electrocatalysts in low‐temperature polymer electrolyte membrane fuel cells. The 9.5 ± 2 nm Au@Pt NPs with atomically thin Pt shells are attached on graphene via l‐cysteine (Cys), which serves as linkers controlling NP loading and dispersion, enhancing the Au@Pt NP stability, and facilitating interfacial electron transfer. The increased activity of G‐Cys‐Au@Pt, compared to non‐chemically immobilized G‐Au@Pt and commercial platinum NPs catalyst (C‐Pt), is a result of (1) the tailored electron transfer pathways of covalent bonds integrating Au@Pt NPs into the graphene framework, and (2) synergetic electronic effects of atomically thin Pt shells on Au cores. Enhanced electrocatalytic oxidation of formic acid, methanol, and ethanol is observed as higher specific currents and increased stability of G‐Cys‐Au@Pt compared to G‐Au@Pt and C–Pt. Oxygen reduction on G‐Cys‐Au@Pt occurs at 25 mV lower potential and 43 A gPt−1 higher current (at 0.9 V vs reversible hydrogen electrode) than for C–Pt. Functional tests in direct fomic acid, methanol and ethanol fuel cells exhibit 95%, 53%, and 107% increased power densities for G‐Cys‐Au@Pt over C–Pt, respectively.

Atomic Carbon Layers Supported Pt Nanoparticles for Minimized CO Poisoning and Maximized Methanol Oxidation

“…Besides their high prices, Pt-based catalysts are susceptible to carbonaceous intermediates, especially CO. For example, the CO adsorption on the Pt surface is especially serious in acidic electrolytes, leading to severe poisoning effect or short life time of these catalysts towards MOR. [4][5][6][7] Design and synthesis of high-performance Pt electrocatalyst for MOR (namely maximized catalytic ability towards MOR but minimized CO poisoning effect during MOR) is thus highly demanded.For such a demand, numerous Pt nanostructures (e.g., hollow nanospheres, [8] nanorods or wires, [9,10] nanoclusters, [11] nanoflowers, [12] octahedral, [13,14] nanosponges, and etc. [15] ) have been synthesized using various approaches.…”

Rh-doped PdAg nanoparticles as efficient methanol tolerance electrocatalytic materials for oxygen reduction

“…A facile wet-chemical approach was used to synthesize Rhdoped PdAg NPs by using palladium(II) acetylacetonate (Pd (acac) 2 ), silver acetate, rhodium(III) acetylacetonate (Rh(acac) 3 ) as the metal precursors, tungsten hexacarbonyl (W(CO) 6 ) as the reducing agent, cetyltrimethyl ammonium bromide (CTAB) as the surfactant, oleic acid (OA) and oleylamine (OAm) as the solvents (Supporting Information). The mixture was heated to 180°C for 3 h in an oil bath.…”

“…To meet the rising demand for energy and reduce the dependence on environmentally unfriendly fossil fuels, the exploration of new efficient energy conversion devices is highly attractive [1][2][3][4][5][6][7]. Direct methanol fuel cells (DMFCs) excel as an ideal solution for energy conversion [8], due to their high reliability, high efficiency and low carbon emission [9].…”

“…Great efforts have been devoted to enhancing the ORR activity of Pt-based multimetallic catalysts by designing hollow [16][17][18], alloy [19][20][21] and core/shell nanostructures [22][23][24], with interesting ligand [25,26], ensemble [27], crystal facet [2,28,29] and strain effects [30,31]. However, because of the methanol crossover [32], the methanol oxidation reaction (MOR) occurs at the cathode [33] and CO intermediates are easily absorbed onto Pt-based surface [34], which results in the CH 3 OH-poisoning [35,36]. What's worse, it brings out a significant degradation of ORR performance and thereby a lower fuel efficiency [37,38].…”

Nanocatalysts for Electrocatalytic Oxidation of Ethanol

“…AuPd coreduction self-supporting nanowire networks 2014 [119] Au@AuPd seed-mediated growth high-indexf acets 2015 [120] AuPd seed-mediated growth Au decoration of Pd at an optimalatomic ratio (Pd 5 Au 1 )2016 [121] AuPd coupling microbials ynthesis with ah ydrothermal process to convert core-shell PdÀAu into AuPd alloy highd ispersion on graphene and heteroatom doping 2016 [122] Au@Pdseed-mediated epitaxialgrowth 4H/fcc [a] crystal-phase heterostructures2017 [123] AuPd seed-mediated growth decoration of Pd nanodendrites on the tips of Au nanowires2017 [124] Au@AuPd seed-mediated growth facet control 2018 [125] AuPd coreductionoptimal atomic Au/Pd ratio to enhancec atalyst stability 2018 [126] Au@Pts urface-limited redox replacement of anu nderpotentially depositedC um onolayer straina nd morphologyeffects2014 [127] AuPt seed-mediated growth morphology control of PtÀAu hetero-nanocrystals 2015 [128] Au@PtP td epositiononA us urfaces throughag alvanice xchanged process with initiallyg rown Cu shells straineffect betweenA ua nd Pt,and heterometallic bonding interactions be-tweenPta nd rGO substrates 2015 [129] AuPt seed-mediated growth to achieve trace Au deposition on commercial Pt/C catalyst bifunctional mechanism that alleviates surface CO poisoning 2015 [130] AuPt CO-mediatedc hemical deposition of Pt quasi-monolayer on Au surfaces electronic effect between quasi-monolayer of Pt and underlyingA u2016 [131] AuPt directional coalescence growth optimal Au/Pt ratio of ultralongAuP talloy wires 2016 [132] Au@Pts eed-mediated growth electronic effectbetween thin Pt shell and underlyingA u2018 [133] PdAg coreductionb yNaBH 4 self-supporting and bifunctional mechanism 2015 [134] PdAg galvanic replacement reaction hollow structure and bifunctional mechanism 2016 [135] PdAg coreductionb yreducingi onic liquid removal of surfacel igands2017 [136] PdAg coreductioni na queousphase 2D dendritesw ith combined electronic and structural effects 2018 [137] PdCo…”