Fe/N/C is a promising non-Pt electrocatalyst for the oxygen reduction reaction (ORR), but its catalytic activity is considerably inferior to that of Pt in acidic medium, the environment of polymer electrolyte membrane fuel cells (PEMFCs). An improved Fe/N/C catalyst (denoted as Fe/N/C-SCN) derived from Fe(SCN)3, poly-m-phenylenediamine, and carbon black is presented. The advantage of using Fe(SCN)3 as iron source is that the obtained catalyst has a high level of S doping and high surface area, and thus exhibits excellent ORR activity (23 A g(-1) at 0.80 V) in 0.1 M H2SO4 solution. When the Fe/N/C-SCN was applied in a PEMFC as cathode catalyst, the maximal power density could exceed 1 W cm(-2).
Early transition metal carbides (TMCs) can be used as supports for platinum-group metals as low-cost electrocatalysts. The determination of electrochemical stability of TMCs is important to identify their potential use in electrochemical and photoelectrochemical applications. Various TMC thin films were synthesized and characterized with Xray diffraction and photoelectron spectroscopy. Chronopotentiometrictitration measurements were used to map the stability regions of the TMC thin films over a wide pH range. The stability of the TMC thin films was correlated to the oxygen binding energy of the parent metal. All of the TMCs studied are stable for hydrogen evolution/oxidation; most are stable for alcohol oxidation, and titanium, tantalum, and zirconium carbides are stable for oxygen evolution/reduction reactions.
N-doped carbon materials
are promising electrocatalysts for oxygen
reduction reaction (ORR). However, the lack of knowledge in the nature
of active sites limits the rational design of this type of catalysts.
Although pyridinic N species are proposed to be active for ORR, little
experimental evidence is provided to reveal the reactive sites. Herein,
we developed a surface-modification method to identify the ortho-carbon atom of the pyridinic ring as the reactive
site for ORR on N-doped graphene. The pyridinic ring of N-doped graphene
was selectively grafted by an acetyl group at pyridinic N and ortho-C atoms by electrophilic and radical substitution,
respectively. The former remained most of ORR catalytic activity,
while the latter lost its activity completely. DFT calculations confirm
that O2 can get adsorbed and reduced favorably on the ortho-C atom of the pyridinic ring. This study provides
new insight into the nature of active sites and the ORR mechanism
for N-doped carbon materials.
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