High pressure pyrolyzed non-precious metal oxygen reduction catalysts for alkaline polymer electrolyte membrane fuel cells

Non-precious metal catalysts, such as metal-coordinated to nitrogen doped-carbon, have shown reasonable oxygen reduction reaction (ORR) performances in alkaline fuel cells. In this report, we present the development of a highly active, stable and low-cost non-precious metal ORR catalyst by direct synthesis under autogenic-pressure conditions. Transmission electron microscopy studies show highly porous Fe-N-C and Co-N-C structures, which were further confirmed by Brunauer-Emmett-Teller surface area measurements. The surface areas of the Fe-N-C and Co-N-C catalysts were found to be 377.5 and 369.3 m2 g-1, respectively. XPS results show the possible existence of N-C and M-Nx structures, which are generally proposed to be the active sites in non-precious metal catalysts. The Fe-N-C electrocatalyst exhibits an ORR half-wave potential 20 mV higher than the reference Pt/C catalyst. The cycling durability test for Fe-N-C over 5000 cycles shows that the half-wave potential lost only 4 mV, whereas the half-wave potential of the Pt/C catalyst lost about 50 mV. The Fe-N-C catalyst exhibited an improved activity and stability compared to the reference Pt/C catalyst and it possesses a direct 4-electron transfer pathway for the ORR process. Further, the Fe-N-C catalyst produces extremely low HO2- content, as confirmed by the rotating ring-disk electrode measurements. In the alkaline fuel single cell tests, maximum power densities of 75 and 80 mW cm-2 were observed for the Fe-N-C and Pt/C cathodes, respectively. Durability studies (100 h) showed that decay of the fuel cell current was more prominent for the Pt/C cathode catalyst compared to the Fe-N-C cathode catalyst. Therefore, the Fe-N-C catalyst appears to be a promising new class of non-precious metal catalysts prepared by an autogenic synthetic method. © The Royal Society of Chemistry 2015.

Insights into N-doping in single-walled carbon nanotubes for enhanced activation of superoxides: A mechanistic study

Emerging characteristics upon nitrogen-doping were differentiated in the activation of superoxides over single-walled carbon nanotubes. Both experimental and theoretical studies revealed that enhanced peroxymonosulfate (PMS) activation is ascribed to a nonradical process while persulfate (PS) activation is accelerated via directly oxidizing water, yet hydrogen peroxide (H2O2) activation is inert to N-doping. This study details the first insights into versatile N-doping in carbocatalysis for organic oxidation in sustainable remediation

Development of Novel Non-precious Cathode Electrocatalysts for Alkaline Exchange Membrane Fuel Cells

DoctordCollectio

Prussian Blue-Carbon Hybrid as a Non-Precious Electrocatalyst for the Oxygen Reduction Reaction in Alkaline Medium

We describe a simple approach for the Prussian blue nanocubes dispersed on carbon composite (PBC/C) as a non-precious catalyst for the electrochemical oxygen reduction reaction (ORR) in alkaline medium. The interaction between Prussian blue (PB) and the carbon support was confirmed by using FT-IR, and XPS spectroscopy. PBC/C catalyst exhibits 100 mV more positive onset potential than Prussian blue supported on carbon (PB/VXC-72) for ORR. Rotating disk electrode measurements showed that PBC/C had about 17 times higher oxygen reduction mass activity compared to the PB/VXC-72 physical mixture. PBC/C hybrid catalyst exhibited superior durability in aqueous alkaline medium compared with Pt/C and also provided low H2O2production confirmed by rotating ring-disk electrode measurement. The PBC/C catalyst showed better activity and selectivity, which can be attributed to the synergistic coupling effects between the PB nanocubes and carbon support. © 2013 Elsevier Ltd.

Hollow nitrogen-doped carbon spheres as efficient and durable electrocatalysts for oxygen reduction

Hollow nitrogen-doped carbon spheres (HNCSs) were prepared by a facile method as non-precious catalysts for the oxygen reduction reaction (ORR). The HNCS catalysts exhibited ORR activity comparable with a commercial Pt/C catalyst and superior stability in alkaline electrolyte medium. This journal is © the Partner Organisations 2014.

Hierarchical Nanostructured Pt8Ti-TiO2/C as an Efficient and Durable Anode Catalyst for Direct Methanol Fuel Cells

A catalyst for the electrochemical oxidation of methanol in direct methanol fuel cells (DMFCs) comprising Pt8Ti intermetallic nanoparticles dispersed in carbon nanorods (Pt8Ti-TiO2/C) is presented. The catalyst consists of Pt8Ti and rutile TiO2 nanoparticles dispersed in nitrogen-doped carbon hierarchical nanostructures. The Pt8Ti-TiO2/C catalyst showed a 50 mV positive onset potential and 10 times higher specific activity than a commercial Pt/C catalyst. Using a half-cell experiment, we show that Pt8Ti intermetallic nanoparticles greatly enhance the methanol oxidation activity and durability in comparison to a Pt/C commercial catalyst. More importantly, a DMFC anode constructed with Pt8Ti-TiO2/C catalyst showed 4.6 times higher power density than a commercial Pt/C catalyst at 0.35 V and 333 K. Additionally, the Pt8Ti-TiO2/C catalyst displayed superior durability in comparison to the Pt/C catalyst. Pt8Ti-TiO2/C showed an electrochemical surface area decay of 23% at the end of 3000 CV cycles, whereas the Pt/C catalyst showed a more rapid decay of 90% at the end of 3000 CV cycles. The excellent stability of the Pt8Ti-TiO2/C catalyst during the accelerated durability stability test (AST) can be attributed to the stability of the rutile TiO2 support, which is chemically resistant in the acidic electrolyte medium. The chronoamperometry and AST durability results confirmed that the Pt8Ti-TiO2/C hierarchical catalyst exhibited better stability than the pure Pt/C catalyst, suggesting that Pt8Ti-TiO2/C could be a promising anode catalyst in DMFCs. © 2015 American Chemical Society.

Investigation of hollow nitrogen-doped carbon spheres as non-precious Fe-N-4 based oxygen reduction catalysts

The development of inexpensive non-precious oxygen reduction catalysts has become one of the most important efforts in polymer electrolyte membrane fuel cells. In this report, we synthesized a non-precious electrocatalyst from a single precursor, iron(iii) diethylene triaminepentaacetate, using a heat-treatment effect to prepare an active catalyst. A series of catalysts were prepared at different temperatures leading to different degrees of graphitization, heteroatom content and activity. In 0.1 M KOH electrolyte solution, the oxygen reduction reaction (ORR) onset potential of the HNCS71 catalyst was as high as 0.97 V, and half-wave potentials were only 20 mV lower than those for Pt/C. X-ray absorption measurements of the Fe K-edge showed the structure of Fe-N<inf>4</inf> centers, formed in HNCS71, which were responsible for the ORR activity. An alkaline exchange membrane fuel cell fabricated with HNCS71 as the cathode was tested in a H<inf>2</inf>-O<inf>2</inf> single cell and showed a maximum power density of ∼68 mW cm-2. The 100 hour fuel cell durability test of the HNCS71 cathode showed a decay in the current density of about 14% at 0.4 V. Therefore, the HNCS catalyst appears to be a promising new class of non-precious catalysts for fuel cell applications. © 2015 Royal Society of Chemistry.

Boron and phosphorous-doped graphene as a metal-free electrocatalyst for the oxygen reduction reaction in alkaline medium

An efficient solid-state pyrolysis route is presented to prepare boron- and phosphorous-doped graphene without using a template, solvent, or catalyst. By controlling the pyrolysis temperature, selective doping of phosphorous or boron was achieved. Phosphorous-doped graphene (PDG) and boron-doped graphene (BDG) samples are obtained when pyrolysing the precursor at 700°C and at 900°C, respectively under autogenic pressure. PDG and BDG electrodes show a considerable oxygen reduction activity by a direct four-electron pathway in alkaline medium. Further, these catalysts show improved durability under continuous oxygen reduction, resistance to methanol oxidation and CO-tolerance than the commercial catalyst. The results suggest that by tuning the reaction temperature, selective doping of either boron or phosphorous in graphene was achieved and the doped graphene samples were used as non-precious and metal-free catalysts for oxygen reduction. © The Royal Society of Chemistry.1

Enhanced Oxygen Reduction Activities of Pt Supported on Nitrogen-Doped Carbon Nanocapsules

The nitrogen-doped carbon nanocapsules (NCNCs) were explored as catalyst support for oxygen reduction reaction (ORR) in acid electrolyte. The deposition of Pt particles on NCNCs support was characterized using various physico-chemical techniques, such as scanning electron microscope, transmission electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy. The high resolution transmission electron microscopy reveals that Pt particles are uniformly dispersed onto the NCNCs and particles size of about 2.2 nm was observed. The electrochemical ORR activities of the Pt supported on NCNCs catalysts were studied and compared with a commercial catalyst. Pt/NCNC showed enhanced ORR activity and better stability than a commercial Pt/C catalyst. The enhanced performance of Pt supported NCNCs can be attributed to the better dispersion and utilization of Pt nanoparticles. © 2014 Elsevier Ltd.