The development of active hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) catalysts for use in anion exchange membrane fuel cells (AEMFCs), which are free from platinum group metals (PGMs), is expected to bring this technology one step closer to commercial applications. This paper reports our recent progress developing HOR Pt-free and PGM-free catalysts (Pd/CeO2 and NiCo/C, respectively), and ORR PGM-free Co3O4 for AEMFCs. The catalysts were prepared by different synthesis techniques and characterized by both physical-chemical and electrochemical methods. A hydrothermally synthesized Co3O4 + C composite ORR catalyst used in combination with Pt/C as HOR catalyst shows good H2/O2 AEMFC performance (peak power density of ~388 mW cm−2), while the same catalyst coupled with our flame spray pyrolysis synthesised Pd/CeO2 anode catalysts reaches peak power densities of ~309 mW cm−2. Changing the anode to nanostructured NiCo/C catalyst, the performance is significantly reduced. This study confirms previous conclusions, that is indeed possible to develop high performing AEMFCs free from Pt; however, the challenge to achieve completely PGM-free AEMFCs still remains.
NbPt 3 intermetallic nanoparticles (NbPt 3 NPs) are synthesized for the first time, and their electrocatalytic performance towards fuel oxidation is tested. Chemical reduction of dichloro(1,5-cyclooctadiene)platinum(II) and niobium(V) pentachloride in dry diglyme with a superhydride, followed by annealing, yields the desired NbPt 3 NPs. These NbPt 3 NPs exhibit higher stability than pure Pt NPs during repeated electrochemical cycles in H 2 SO 4 . The NbPt 3 NPs are less susceptible to CO adsorption compared with Pt NPs and exhibit improved catalytic activity towards the electrooxidation of ethanol and/or formic acid. These NbPt 3 NPs are promising candidates as electrode catalysts in fuel cells.Metal catalysts may play a central role in exhaust purification and chemical industries, but they are also important in the sustainable-energy technologies including photocatalytic water splitting and polymer electrolyte membrane fuel cells (PEMFCs). [1] Pt is one of the most efficient catalytic metals, which enables direct chemical-energy conversion in PEMFCs at a much higher efficiency than combustion engines. [2] However, Pt-based metal catalysts are highly susceptible to poisoning by carbon monoxide contained in the fuels (CO poisoning). [3] Alloying Pt with late transition metals and/or metalloids, including Ru, Fe, Co, Ni, Cu or Sn, can improve the poisoning tolerance as well as the catalytic performance, but causes poor stability of the catalysts through surface segregation; the counter elements of Pt readily migrate into the bulk and/or leach out of the alloy during long-term operation. [4, 5] Intermetallic compounds of Pt with early transition metals can act as more stable electrode catalysts than conventional late-transition-metal alloys because of their large enthalpy of formation (DH f ), for example DH f = À46.6 kJ mol À1 for Nb in NbPt 3 compared with DH f = À13.6 kJ mol À1 for Fe in Fe-Pt alloys. [6,7] Moreover, Pt nanoparticles (NPs) supported by niobium oxides have exhibited enhanced anodic and/or cathodic activities in acidic media, suggesting that the alloying of Nb and Pt at the interface may improve electrocatalytic performance. [8] However, no Nb-containing metal catalysts have been materialized to date, because Nb metal is extremely airsensitive in the form of fine particles or porous materials. Herein, we demonstrate that NbPt 3 intermetallic NPs can be synthesized through a wet-chemistry route and exhibit improved stability, CO-poisoning tolerance, and enhanced electrooxidation activity for carbon-containing fuels, that is, ethanol and formic acid, in PEMFCs.NbPt 3 NPs were synthesized through the chemical reduction of dichloro(1,5-cyclooctadiene)platinum(II) [Pt(COD)Cl 2 ] and niobium(V) pentachloride (NbCl 5 ) in dry diglyme [1-methoxy-2-(2-methoxyethoxy)ethane] with a superhydride [LiB-(CH 3 CH 2 ) 3 H], which was followed by annealing in an Ar flow (Scheme 1). Stoichiometric amounts of Pt(COD)Cl 2 (0.12 mmol) and NbCl 5 (0.04 mmol) were dissolved in dry diglyme (30 mL) under a pure Ar atmosp...
The latest progress in alkaline anion-exchange membranes has led to the expectation that less costly catalysts than those of the platinum-group metals may be used in anion-exchange membrane fuel cell devices. In this work, we compare structural properties and the catalytic activity for the hydrogen-oxidation reaction (HOR) for carbon-supported nanoparticles of Ni, Ni 3 Co, Ni 3 Cu, and Ni 3 Fe, synthesized by chemical and solvothermal reduction of metal precursors. The catalysts are well dispersed on the carbon support, with particle diameter in the order of 10 nm, and covered by a layer of oxides and hydroxides. The activity for the HOR was assessed by voltammetry in hydrogen-saturated aqueous solutions of 0.1 mol dm –1 KOH. A substantial activation by potential cycling of the pristine catalysts synthesized by solvothermal reduction is necessary before these become active for the HOR; in situ Raman spectroscopy shows that after activation the surface of the Ni/C, Ni 3 Fe, and Ni 3 Co catalysts is fully reduced at 0 V, whereas the surface of the Ni 3 Cu catalyst is not. The activation procedure had a smaller but negative impact on the catalysts synthesized by chemical reduction. After activation, the exchange-current densities normalized with respect to the ECSA (electrochemically active surface area) were approximately independent of composition but relatively high compared to catalysts of larger particle diameter.
Tin-dioxide nanofacets (SnO2 NFs) are crystal-engineered so that oxygen defects on the maximal {113} surface are long-range ordered to give rise to a non-occupied defect band (DB) in the bandgap. SnO2 NFs-supported platinum-nanoparticles exhibit an enhanced ethanol-electrooxidation activity due to the promoted charge-transport via the DB at the metal-semiconductor interface.
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