Effect of Precursor Status on the Transition from Complex to Carbon Shell in a Platinum Core-Carbon Shell Catalyst.

Encapsulating platinum nanoparticles with a carbon shell can increase the stability of core platinum nanoparticles by preventing their dissolution and agglomeration. In this study, the synthesis mechanism of a platinum core-carbon shell catalyst via thermal reduction of a platinum-aniline complex was investigated to determine how the carbon shell forms and identify the key factor determining the properties of the Pt core-carbon shell catalyst. Three catalysts originating from the complexes with different platinum to carbon precursor ratios were synthesized through pyrolysis. Their structural characteristics were examined using various analysis techniques, and their electrochemical activity and stability were evaluated through half-cell and unit-cell tests. The relationship between the nitrogen to platinum ratio and structural characteristics was revealed, and the effects on the electrochemical activity and stability were discussed. The ratio of the carbon precursor to platinum was the decisive factor determining the properties of the platinum core-carbon shell catalyst.

A nitrogen and fluorine enriched Fe/Fe3C@C oxygen reduction reaction electrocatalyst for anion/proton exchange membrane fuel cells.

Nitrogen-doped carbon-encapsulated non-noble metals are promising electrocatalytic alternatives to Pt for the oxygen reduction reaction (ORR). Herein, we describe the efficient synthesis of nitrogen- and fluorine-doped carbon-encapsulated Fe/Fe3C (NFC@Fe/Fe3C) crystals from a Fe-poly(aniline-fluoro-aniline) co-polymer and demonstrate their use as efficient ORR electrocatalysts in acidic and alkaline environments. X-ray diffraction patterns, scanning electron microscopy, transmission electron microscopy, Raman spectra, and X-ray photoelectron spectroscopy are used to determine the structural properties of NFC@Fe/Fe3C. Of the NFC@Fe/Fe3C catalysts, NFC@Fe/Fe3C-9 demonstrates superior ORR electrocatalytic activity in both alkaline and acidic environments. NFC@Fe/Fe3C-9 follows a four-electron-transfer ORR pathway in alkaline and acidic media. Under alkaline conditions, NFC@Fe/Fe3C-9 displays a half-wave potential (E1/2) as 0.870 V, which is 16 mV higher than that of Pt/C, and its durability decay is 26 mV over 50 000 cycles. In acidic medium, the NFC@Fe/Fe3C-9 electrode shows inferior ORR performance than does Pt/C, but it is more durable, with only 27 mV decay over 30 000 cycles. A single cell performance of NFC@Fe/Fe3C-9 was tested with a proton-exchange membrane fuel cells (PEMFC) and an anion-exchange membrane fuel cell (AEMFC) with an active area of 5 cm2. The PEMFC single cell exhibits the maximum power density of 237 mW cm-2 with a back pressure of 250 kPa, while the AEMFC delivers a maximum power density of 96 mW cm-2 without back pressure.

Ultrafine Pt Nanoparticles Stabilized by MoS2/N-Doped Reduced Graphene Oxide as a Durable Electrocatalyst for Alcohol Oxidation and Oxygen Reduction Reactions.

Direct alcohol fuel cells play a pivotal role in the synthesis of catalysts because of their low cost, high catalytic activity, and long durability in half-cell reactions, which include anode (alcohol oxidation) and cathode (oxygen reduction) reactions. However, platinum catalysts suffer from CO tolerance, which affects their stability. The present study focuses on ultrafine Pt nanoparticles stabilized by flowerlike MoS2/N-doped reduced graphene oxide (Pt@MoS2/NrGO) architecture, developed via a facile and cost-competitive approach that was performed through the hydrothermal method followed by the wet-reflux strategy. Fourier transform infrared spectra, X-ray diffraction patterns, Raman spectra, X-ray photoelectron spectra, field-emission scanning electron microscopy, and transmission electron microscopy verified the conversion to Pt@MoS2/NrGO. Pt@MoS2/NrGO was applied as a potential electrocatalyst toward the anode reaction (liquid fuel oxidation) and the cathode reaction (oxygen reduction). In the anode reaction, Pt@MoS2/NrGO showed superior activity toward electro-oxidation of methanol, ethylene glycol, and glycerol with mass activities of 448.0, 158.0, and 147.0 mA/mgPt, respectively, approximately 4.14, 2.82, and 3.34 times that of a commercial Pt-C (20%) catalyst. The durability of the Pt@MoS2/NrGO catalyst was tested via 500 potential cycles, demonstrating less than 20% of catalytic activity loss for alcohol fuels. In the cathode reaction, oxygen reduction reaction results showed excellent catalytic activity with higher half-wave potential at 0.895 V versus a reversible hydrogen electrode for Pt@MoS2/NrGO. The durability of the Pt@MoS2/NrGO catalyst was tested via 30 000 potential cycles and showed only 15 mV reduction in the half-wave potential, whereas the Pt@NrGO and Pt-C catalysts experienced a much greater shift (Pt@NrGO, ∼23 mV; Pt-C, ∼20 mV).