Sujan Shrestha

Properties of Nitrogen-Functionalized Ordered Mesoporous Carbon Prepared Using Polypyrrole Precursor

Nitrogen-doped ordered mesoporous carbon was synthesized using SBA-15 as the template and polypyrrole as the nitrogen-containing carbon precursor. Transmission electron microscopy and N 2 Brunauer, Emmett, and Teller adsorption revealed a honeycomb-like ordered mesoporous structure with an average pore diameter of 3.3 nm with a narrow distribution. X-ray photoelectron spectroscopy showed that pyridinic and quaternary nitrogen functionalities were the dominant nitrogen surface functional groups. A high percentage of nitrogen was retained in the carbon surface (C/N = 8.3). The prepared nitrogen-functionalized support had a specific double layer capacitance of 182.5 F/g. Also, its intrinsic oxygen reduction activity was better than that of Vulcan XC-72R. Accelerated degradation test showed that nitrogen-functionalized carbon was highly resistant to electrochemical corrosion.

Electrocatalytic Activity and Stability of Pt clusters on State-of-the-Art Supports: A Review

Instability of supported Pt clusters due to limited bonding with conventional carbon supports and carbon dissolution leads to significant cathode performance losses with time, impeding the development of commercial proton exchange membrane fuel cells. One approach that has recently been gaining momentum is the use of the electrocatalyst support to enhance both the stability and activity of Pt clusters for the oxygen reduction reaction. This review article focuses on four support types: advanced carbons, conductive ceramics, metallic underlayers for Pt monolayer catalysts, and the 3M crystalline organic whiskers. Advantages and disadvantages of each support are summarized and promising future directions for research in this area are discussed.

Platinum–copper nanotube electrocatalyst with enhanced activity and durability for oxygen reduction reactions

The activity and the durability of Pt based electrocatalysts constitute the major challenges in the current fuel cell technology. Motivated by the improved activity and ameliorated durability for Pt based cathode catalysts achieved from the compositional and morphological control, respectively, in this paper, a rationally designed, PtCu based, 1-dimensional electrocatalyst was prepared via a facile and scalable procedure. The detailed materials characterization revealed that the as-prepared nanotubes (NTs) were composed of a PtCu alloy bulk and a Pt-enriched surface with downshifted d-band center position. Towards the electrocatalysis of oxygen reduction reaction, PtCu NTs have displayed a distinguished specific activity with more than a 10-fold improvement relative to the commercial catalysts and more than a 3-fold improvement relative to the 2015 DOE technical target (0.72 mA cmPt−2 @ 0.9 V). Meanwhile, PtCu NTs have shown greatly ameliorated durability in the aspects of both ECSA and mass activity compared to Pt/C (40%) and Pt black after a 6000-cycle accelerated durability test.

Effect of surface chemistry on the double layer capacitance of polypyrrole-derived ordered mesoporous carbon

In this work, the effect of nitrogen on the double layer (DL) capacitance of nitrogen-doped ordered mesoporous carbon (NOMC) is studied. The nitrogen content of the NOMCs was controlled thermally. X-ray photoelectron spectroscopy shows decreasing nitrogen content with increasing heat treatment temperature. Despite the differing N content of the NOMCs, the BET surface area, pore size and distribution of the NOMCs did not change significantly with the heat treatment, though Raman spectroscopy and X-ray diffraction showed that the microcrystallinity was affected, exposing more of the basal planes with increased heat treatment temperature. The DL capacitance of the NOMCs was measured from cyclic voltammograms in a range that minimized the contribution of the space charge capacitance and pseudocapacitance, yielding information about the impact of oxygen and nitrogen functional groups on the pure Helmholtz behavior of NOMCs. It was found that nitrogen affects the DL capacitance by changing both the electronic properties and microstructure of the carbon. These enhancements resulted in NOMCs with very high areal Helmholtz capacitance of 25.1 μF cm−2.

ORR and Fuel Cell Performance of Pt Supported on N-Functionalized Mesoporous Carbon

Nitrogen functionalized ordered mesoporous carbon (NOMC) was synthesized and decorated with Pt nanoparticles using a modified polyol process. After characterizing porosity and surface chemistry, their activity towards oxygen reduction reaction was studied using a thin-film rotating disk electrode and as a cathode in a proton exchange membrane fuel cell. In both tests, lower specific activity but higher mass-specific activities were found for Pt/NOMC compared to Pt/Vulcan carbon.

Platinum Nanoparticles Supported on N-Functionalized Mesoporous Carbon

A modified polyol process was used to deposit platinum nanoparticles on nitrogen functionalized ordered mesoporous carbon. The pH was adjusted to control the platinum size and loading. Several physical characterization tools were used to determine the size, dispersion and structure of the catalyst and support including X-ray Photoelectron Spectroscopy, X-ray Diffraction, and high resolution transmission electron microscopy. The electrochemically active area for the oxygen reduction reaction was computed by cyclic voltammetry. Platinum deposited on nitrogen functionalized ordered mesoporous carbon was found to have higher dispersion and utilization than platinum deposited on Vulcan XC-72R.

Promises and Challenges of Unconventional Electrocatalyst Supports

One of the most significant roadblocks in the commercialization and widespread implementation of proton exchange membrane fuel cells is the identification of low-cost, high-stability, high-activity electrocatalysts. An overwhelming amount of the work that has been done in this area has targeted the electrochemically active material, which has been the focus of much of this book. However, a key component to any catalyst is its support. Interaction between the catalyst and support dictates some of the most critical parameters for fuel cell performance including catalyst dispersion, particle size, faceting, and stability. Some supports, like graphitic carbon, interact very weakly with Pt and have a limited influence on catalyst activity and stability. On the other hand, recent work by several groups has shown that a strongly interacting support can drastically impact both catalyst activity and stability.