Hexiang Zhong

Nitrogen-doped carbon xerogel: A novel carbon-based electrocatalyst for oxygen reduction reaction in proton exchange membrane (PEM) fuel cells

A low-cost, novel carbon-based electrocatalyst for oxygen reduction reaction (ORR), nitrogen-doped carbon xerogel (N-CX) was synthesized via a sol–gel polymerization method followed by a pyrolysis process. The N-CX catalyst exhibited a high activity for ORR, and a good stability in acid media. A high performance with a maximum power density of 360 mW cm−2 was achieved on a single PEM fuel cell with N-CX as the cathode electrocatalyst.

Nitrogen-Enriched Carbon from Melamine Resins with Superior Oxygen Reduction Reaction Activity

Catalytic carbon: Nitrogen-doped porous carbon (CN(x)) electrocatalysts are derived from inexpensive melamine formaldehyde resins. These potential PEMFC catalysts are synthesized by using a facile method, which yields materials that contain a meso- and macroporous structure. The carbon-based materials display attractive catalytic activity toward ORR and superior stability compared to a commercial Pt-based catalyst.

Nitrogen-doped hierarchically porous carbon as efficient oxygen reduction electrocatalysts in acid electrolyte

Nitrogen-doped carbon was found to exhibit excellent activity as an electrocatalyst in renewable energy devices. A controllable method to synthesize N-doped hierarchically porous carbons (PNCEs) partly with graphene-like structure using polyaniline (PANI)–polyvinylpyrrolidone (PVP) composite as a carbon source via a soft-template process was reported. The catalytic mechanism was thoroughly studied to better understand the relationship between the structure, Fe species and catalytic activity. The PNCE prepared at 1000 °C displays the best performance achieving a maximum power density of 456 mW cm−2 and oxygen reduction reaction (ORR) onset potential of 0.90 V. More prominently, the catalyst presents superior stability, as well as poison tolerance including methanol and SO2 to the commercial JM-Pt/C catalyst in 0.5 M H2SO4. The PVP is proven to tailor the structure, improve the surface area, and alter the transition metal species. The PNCEs synthesized under NH3 exhibit considerably better catalytic activity toward ORR compared with the undoped carbon and PNCEs synthesized under an N2 atmosphere. Furthermore, we find that the nitrogen bonding configurations, textural structure, Fe species and surface areas of PNCEs play key roles in the electrocatalytic activity towards the ORR. The formed FeN4 species hosted in the micropores acts as the active component for ORR activity in PNCEs, although it is not the only contributor to the high performance of PNCEs. The catalyst is expected to be a promising non-noble electrocatalyst for use in polymer electrolyte membrane fuel cells.

A Nitrogen-Doped Polyaniline Carbon with High Electrocatalytic Activity and Stability for the Oxygen Reduction Reaction in Fuel Cells

PANI-BASED CARBON CAT: A low-cost nitrogen-doped carbon nanomaterial from polyaniline as fuel cell cathode electrocatalyst is prepared by chemical polymerization of aniline monomers, followed by pyrolysis in the presence of ammonia. The catalyst demonstrates high activity, with an onset potential comparable to, and a reduction current higher than, a commercial platinum catalyst.

Bismuth nanodendrites as a high performance electrocatalyst for selective conversion of CO2 to formate

A nanostructured bismuth dendrite catalyst was designed and directly grown on treated carbon paper using a novel electrochemical deposition method. It exhibits an excellent performance for efficient CO2 reduction to formate, achieving a maximum faradaic efficiency of 96.4% with a current density of 15.2 mA cm−2. The catalyst is shown to be stable during 10 h of continuous electrolysis.

Zn electrode with a layer of nanoparticles for selective electroreduction of CO2 to formate in aqueous solutions

Developing inexpensive and non-toxic electrocatalysts that can reduce CO2 to formate with high selectivity and stability as well as high current densities is an important step for a sustainable carbon cycle. Electrocatalysts that show the highest faradaic efficiency for formate, such as Pb and Hg, are toxic or expensive and have low current densities. Bulk Zn is a cheap metal that has historically been identified to be a CO2 to CO conversion catalyst. In this work, we introduce a novel Zn electrode with a layer of nanoparticles that exhibit high performance toward CO2 electrochemical reduction to produce formate in aqueous solution. The maximum faradaic efficiency for formate production of over 87% is achieved with a formate partial current density of 12.8 mA cm−2, which are almost 8 times higher than that of bulk Zn foil and 17 times higher than that of bulk Zn foil, respectively. The improvement in catalytic performance is attributed to the catalytically active facets and special surface structure of polycrystalline Zn formed during reduction of polycrystalline ZnO. The catalyst shows no obvious performance deterioration during the 14 h continuous CO2 reduction.

Ordered Hierarchically Porous Carbon Codoped with Iron and Nitrogen as Electrocatalyst for the Oxygen Reduction Reaction

N-doped carbon catalysts have attracted great attention as potential alternatives to expensive Pt-based catalysts used in fuel cells. Herein, an ordered hierarchically porous carbon codoped with N and Fe (Fe-NOHPC) is prepared by an evaporation-induced self-assembly process followed by carbonization under ammonia. The soft template and Fe species promote the formation of the porous structure and facilitate the oxygen reduction reaction (ORR).The catalyst possesses an ordered hierarchically porous structure with a large surface area (1172.5 m(2) g(-1) ) and pore volume of 1.03 cm(3) g(-1) . Compared to commercial 20% Pt/C, it exhibits better ORR catalytic activity and higher stability as well as higher methanol tolerance in an alkaline electrolyte, which demonstrates its potential use in fuel cells as a nonprecious cathode catalyst. The N configuration, Fe species, and pore structure of the catalysts are believed to correlate with its high catalytic activity.

Selective Electrochemical Reduction of Carbon Dioxide Using Cu Based Metal Organic Framework for CO2 Capture

The conversion efficiency and product selectivity of the electroreduction of carbon dioxide have been largely limited by the low CO2 solubility in aqueous solution. To relieve this problem, Cu3(BTC)2 (Cu-MOF) as CO2 capture agent was introduced into a carbon paper based gas diffusion electrode (GDE) in this study. The faradaic efficiencies (FEs) of CH4 on GDE with Cu-MOF weight ratio in the range of 7.5-10% are 2-3-fold higher than that of GDE without Cu-MOF addition under negative potentials (-2.3 to -2.5 V vs SCE), and the FE of the competitive hydrogen evolution reaction (HER) is reduced to 30%. This work paves the way to develop GDE with high catalytic activity for ERC.

Mn x Ir 1−x O 2 /C used as bifunctional electrocatalyst in alkaline medium

There is a growing interest in oxygen electrochemistry as conversions between O₂ and H₂O play an important role in a variety of renewable energy technologies. In this paper, bifunctional electrocatalysts of the general formula Mn_xIr_1-xO₂/C were prepared using a pyrolysis method. Their physical characteristics were examined via transmission electron microscopy, and the electrochemical properties were examined via cyclic voltammetry and linear sweep voltammetry measurements in 1M KOH solution. Experimental results show that with the content of iridium increasing in Mn_xIr_1-xO₂/C, the oxygen reduction reaction (ORR) activity first increases and then decreases. Mn_0.75Ir_0.25O₂/C has the highest ORR activity and its half-wave potential obtains -0.071V (relative to Hg/HgO electrode). It is worth noting that doping the MnO₂/C nanoparticles with only a small amount of iridium can considerably improve the oxygen evolution reaction (OER) activity of MnO₂ in the alkaline medium. The oxygen evolution current density at 0.75 V vs. Hg/HgO of Mn_0.75Ir_0.25O₂/C was nearly 4.31 times as that of MnO₂/C. The results offer an important direction for the development of bifunctional oxygen catalysts in alkaline medium.