Guoxiong Wang

Iron Encapsulated within Pod-like Carbon Nanotubes for Oxygen Reduction Reaction

Chainmail for catalysts: a catalyst with iron nanoparticles confined inside pea-pod-like carbon nanotubes exhibits a high activity and remarkable stability as a cathode catalyst in polymer electrolyte membrane fuel cells (PEMFC), even in presence of SO(2). The approach offers a new route to electro- and heterogeneous catalysts for harsh conditions.

Size-Dependent Electrocatalytic Reduction of CO2 over Pd Nanoparticles

Size effect has been regularly utilized to tune the catalytic activity and selectivity of metal nanoparticles (NPs). Yet, there is a lack of understanding of the size effect in the electrocatalytic reduction of CO2, an important reaction that couples with intermittent renewable energy storage and carbon cycle utilization. We report here a prominent size-dependent activity/selectivity in the electrocatalytic reduction of CO2 over differently sized Pd NPs, ranging from 2.4 to 10.3 nm. The Faradaic efficiency for CO production varies from 5.8% at -0.89 V (vs reversible hydrogen electrode) over 10.3 nm NPs to 91.2% over 3.7 nm NPs, along with an 18.4-fold increase in current density. Based on the Gibbs free energy diagrams from density functional theory calculations, the adsorption of CO2 and the formation of key reaction intermediate COOH* are much easier on edge and corner sites than on terrace sites of Pd NPs. In contrast, the formation of H* for competitive hydrogen evolution reaction is similar on all three sites. A volcano-like curve of the turnover frequency for CO production within the size range suggests that CO2 adsorption, COOH* formation, and CO* removal during CO2 reduction can be tuned by varying the size of Pd NPs due to the changing ratio of corner, edge, and terrace sites.

Li / Li1 + x V 3 O 8 Secondary Batteries Synthesis and Characterization of an Amorphous Form of the Cathode

This paper reports a new synthesis route applied to obtain Li{sub 1+x}V{sub 3}O{sub 8}. Instead of the conventional high-temperature technique leading to the crystalline form, a solution technique producing the amorphous form has been used. This material, after dehydration, shows an electrochemical performance exceeding that of the crystalline one. The rationale for this behavior mainly lies in the microscopic factors, i.e., in the possibility for the unit cell of amorphous Li{sub 1+x}V{sub 3}O{sub 8} to insert up to 9 Li{sup +}, instead of six for crystalline Li{sub 1+x}V{sub 3}O{sub 8}. Furthermore, the absence of a long-range crystallographic order reduces the length of the pathways through which Li{sup +} ions diffuse. This and the favorable morphology endow amorphous Li{sub 1+x}V{sub 3}O{sub 8} with a high rate capability. The higher energy content afforded by this new form (theoretical value, 935 Wh/kg, based on the electrodes weight) can be exploited in long-cycling cells at high rates.

Cobalt nanoparticles encapsulated in nitrogen-doped carbon as a bifunctional catalyst for water electrolysis

The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are important electrocatalytic processes in water electrolyzers. Identifying efficient non-precious metal catalysts for HER and OER remains a great challenge for applications in different kinds of electrolyzers. Herein, we report that cobalt nanoparticles encapsulated in nitrogen-doped carbon (Co@N–C) show high activity and durability for HER in a wide pH range and for OER in alkaline medium as a bifunctional catalyst. The HER and OER activities of Co@N–C are higher than those of multiwall carbon nanotube and iron nanoparticles encapsulated in nitrogen-doped carbon with a similar content of nitrogen. Electrolyzer prototypes using Nafion NRE-212 as electrolyte membrane and Co@N–C as cathode or anode catalyst are constructed, showing potential practical applications in water splitting.

Novel synthesis of highly active Pt/C cathode electrocatalyst for direct methanol fuel cell

A 40 wt% Pt/C cathode electrocatalyst with controlled Pt particle size of approximately 2.9 nm showing better performance than commercial catalyst for direct methanol fuel cell was prepared by a polyol process with water but without using stabilizing agent.

One-Pot Synthesis of Highly Anisotropic Five-Fold-Twinned PtCu Nanoframes Used as a Bifunctional Electrocatalyst for Oxygen Reduction and Methanol Oxidation.

Five-fold-twinned PtCu nanoframes (NFs) with nanothorns protruding from their edges are synthesized by a facile one-pot method. Compared to commercial Pt/C catalyst, the obtained highly anisotropic five-fold-twinned PtCu NFs show enhanced electrocatalytic performance toward the oxygen reduction reaction and methanol oxidation reaction under alkaline conditions.

Highly doped and exposed Cu(I)–N active sites within graphene towards efficient oxygen reduction for zinc–air batteries

A coordinatively unsaturated copper–nitrogen architecture in copper metalloenzymes is essential for its capability to catalyze the oxygen reduction reaction (ORR). However, the stabilization of analogous active sites in realistic catalysts remains a key challenge. Herein, we report a facile route to synthesize highly doped and exposed copper(I)–nitrogen (Cu(I)–N) active sites within graphene (Cu–N©C) by pyrolysis of coordinatively saturated copper phthalocyanine, which is inert for the ORR, together with dicyandiamide. Cu(I)–N is identified as the active site for catalyzing the ORR by combining physicochemical and electrochemical studies, as well as density function theory calculations. The graphene matrix could stabilize the high density of Cu(I)–N active sites with a copper loading higher than 8.5 wt%, while acting as the electron-conducting path. The ORR activity increases with the specific surface area of the Cu–N©C catalysts due to more exposed Cu(I)–N active sites. The optimum Cu–N©C catalyst demonstrates a high ORR activity and stability, as well as an excellent performance and stability in zinc–air batteries with ultralow catalyst loading.

Enhancing CO2 Electroreduction with the Metal–Oxide Interface

The electrochemical CO2 reduction reaction (CO2RR) typically uses transition metals as the catalysts. To improve the efficiency, tremendous efforts have been dedicated to tuning the morphology, size, and structure of metal catalysts and employing electrolytes that enhance the adsorption of CO2. We report here a strategy to enhance CO2RR by constructing the metal-oxide interface. We demonstrate that Au-CeOx shows much higher activity and Faradaic efficiency than Au or CeOx alone for CO2RR. In situ scanning tunneling microscopy and synchrotron-radiation photoemission spectroscopy show that the Au-CeOx interface is dominant in enhancing CO2 adsorption and activation, which can be further promoted by the presence of hydroxyl groups. Density functional theory calculations indicate that the Au-CeOx interface is the active site for CO2 activation and the reduction to CO, where the synergy between Au and CeOx promotes the stability of key carboxyl intermediate (*COOH) and thus facilitates CO2RR. Similar interface-enhanced CO2RR is further observed on Ag-CeOx, demonstrating the generality of the strategy for enhancing CO2RR.

Performance improvement in direct methanol fuel cell cathode using high mesoporous area catalyst support

black pearls 2000 (designated as bp- 2000) and vulcan xc-72 (designated as xc-72) carbon blacks were chosen as supports to prepare 40 wt % (the targeted value) pt/c catalysts by a modified polyol process. the carbon blacks were characterized by n-2 adsorption and fourier tranform infrared spectroscopy. the prepared catalysts were characterized by inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy, scanning electron microscopy (sem), in situ cyclic voltammetry, and current-voltage curves. on bp- 2000, pt nanoparticles were larger in size and more unevenly distributed than on xc-72. it was observed by sem that the corresponding catalyst layer on bp- 2000 was thicker than that of xc-72 based catalyst at almost the identical catalyst loading. and the bp- 2000 supported catalyst gave a better single cell performance at high current densities. these results suggest that the performance improvement is due to the enhanced oxygen diffusion and water removal capability when bp- 2000 is used as cathode catalyst support. (c) 2004 the electrochemical society.

Preparation of highly active Pt/C cathode electrocatalysts for DMFCs by an improved aqueous impregnation method

An improved aqueous impregnation method was used to prepare 40 wt% Pt/C electrocatalysts. TEM analysis of the samples showed that the Pt particles impregnated for a short time have a very narrow size distribution in the range of 1–4 nm with an average size of 2.6 nm. UV-vis spectroscopy measurements verified that the redox reaction between PtCl62− and formaldehyde took place with a slow rate at ambient temperature via a two-step reaction path, where PtCl42− serves as an intermediate. The use of the short-time-impregnated 40 wt% Pt/C as cathode electrocatalysts in direct methanol fuel cells yields better performance than that of commercial 40 wt% Pt/C electrocatalyst. Experimental evidence provides clues for the fundamental understanding of elementary steps of the redox reactions, which helps in guiding the design and preparation of highly dispersed Pt catalyst for fuel cells.