Nitrogen-doped graphene anchored with mixed growth patterns of CuPt alloy nanoparticles as a highly efficient and durable electrocatalyst for the oxygen reduction reaction in an alkaline medium (original) (raw)
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Iron and nitrogen co-doped carbon catalysts (Fe/N/C catalysts) are promising nonprecious-metal catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. Understanding the ORR kinetics over Fe/N/C catalysts is crucial for active catalyst development. Here, we propose an analytical method for rotating ring-disk electrode (RRDE) voltammetry to separate the ORR for O 2 reduction to H 2 O via the 4-e pathway (k 1), O 2 reduction to H 2 O 2 via the 2-e pathway (k 2), H 2 O 2 reduction to H 2 O via the 2-e pathway (k 3), H 2 O 2 chemical decomposition to O 2 and H 2 O (k 4), and H 2 O 2 oxidation to O 2 by the 2-e pathway (k-2). First, RRDE voltammetry in an H 2 O 2 solution was performed, yielding k 3 , k 4 , and k-2. The obtained parameters were used to analyze the ORR voltammogram to calculate I 1 ′, I 2 ′, I 3 ′, I 4 ′, k 1 ′, and k 2 ′. These currents and kinetic constants were corrected by studying the effect of the catalyst loading density to obtain I 1 0 , I 2 0 , I 3 0 , I 4 0 , k 1 0 , and k 2 0 , thus avoiding the overestimation of I 1 0 and k 1 0 caused by the quasi-four-electron reduction of O 2. The contribution of k 4 during the ORR is negligible at
Analytical Chemistry
Thin film-rotating disc electrode (TF-RDE) experiment provides a fast research platform for screening of newly developed electrocatalysts for oxygen reduction reaction (ORR) activity, however, precise estimation of their performance parameters is necessary to avoid wastage of resources in the testing of otherwise unpromising electrocatalyst in actual fuel cells. Here we show the importance of the accurate amount of catalyst (e.g. Pt) on glassy carbon (GC) disk of RDE in TF-RDE experiment by characterizing the commercial catalysts for their electrocatalysis performance (electrochemical surface area and ORR activity) values. The Pt loadings used to calculate these performance values were obtained using two schemes, namely, using the literature based (conventional) scheme and an X-ray fluorescence (XRF) based scheme. A parameter called 'catalyst-density-ofthe-ink' is used to correlate the variations observed in performance values and the amount of Pt on GC disk of RDE obtained using both the schemes. The investigation suggests that the actual Pt loading on GC disk of RDE varies with the ink-conditions, which is considered constant in the conventional scheme and might be one of the reasons of irreproducibility of the data obtained by TF-RDE experiments. The XRF based scheme, which is simple and direct, can have the potential to replace conventional scheme for accurate catalyst loading estimation, improve experimental reproducibility and open many other possibilities (e.g. postmortem analysis of catalyst) in electrocatalysis studies.
Journal of Solid State Electrochemistry, 2015
This work summarizes progresses achieved in electrochemical oxygen transfer reactions from water to organic pollutant molecules on metal oxide electrodes during the past two decades. Fundamental understanding of the dynamics of the electrochemical oxygen transfer reaction is of crucial importance for the development of key concepts of electrocatalytic processes, leading to the implementation of environmental electrochemistry wastewater treatment schemes with rational design of the suitable electrocatalytic systems. We discuss the current knowledge on the electrochemical oxygen transfer reaction, emphasizing the importance of surface processes in order to generalize mechanistically the experimental results obtained on different electrode materials, describing also the practical kinetic models developed and their implications. From the information gathered in this review, it is apparent that explanations for the kinetics of the reactions in relation to the structure of the organic compounds involved is lacking, hence that new information about structure-reactivity relationships is needed. We show in particular that the open circuit decay of the concentration of radical cations, obtained from spectroelectrochemical data, allows correlating the structure of adsorbed states with reactivity during oxygen transfer reactions, pointing as well to research efforts required to understand the catalytic performance of metal oxide electrodes in decomposing organic compounds strongly adsorbed on their surfaces. Finally, some perspectives for future research in this area are briefly commented.
Journal of the Electrochemical Society, 2015
Oxygen reduction reaction (ORR) in acidic media is investigated at various potentials in a thin-film rotating disk electrode (TF-RDE) configuration using electrochemical impedance spectroscopy (EIS). The ionomer-free and ionomer-containing thin-film catalyst layers are composed of Pt black and carbon-supported Pt catalysts of different metal loadings (5 and 20 wt%). The simplest EI spectrum consisting of an arc or a semi-circle is obtained at high potentials with ionomer-free Pt catalyst layers. The most complex spectrum consisting of a high frequency (HF) arc and two semi-circles is observed in the mixed diffusion-controlled region of the ionomer-containing catalyst layer with high loading of carbon-supported Pt. The nature of the EI spectrum is decided by the constituents of the thin-film catalyst layer and by the operating potential. The evolution of the EI spectra with ionomer and carbon contents is underlined. The effect of rotation rate (rpm) of the electrode on the impedance spectrum is also investigated. A series of equivalent circuits is required to completely describe the EI spectra of ORR. The kinetic parameters and the electrochemical surface area of the catalysts are derived from the impedance spectrum.
Angewandte Chemie International Edition, 2006
The fuel cell is a promising alternative to environmentally unfriendly devices that are currently powered by fossil fuels. In the polymer electrolyte membrane fuel cell (PEMFC), the main fuel is hydrogen, which through its reaction with oxygen produces electricity with water as the only by-product. To make PEMFCs economically viable, there are several problems that should be solved; the main one is to find more effective catalysts than Pt for the oxygen reduction reaction (ORR), 1/2 O 2 + 2 H + + 2 e À = H 2 O. The design of inexpensive, stable, and catalytically active materials for the ORR will require fundamental breakthroughs, and to this end it is important to develop a fundamental understanding of the catalytic process on different materials. Herein, we describe how variations in the electronic structure determine trends in the catalytic activity of the ORR across the periodic table. We show that Pt alloys involving 3d metals are better catalysts than Pt because the electronic structure of the Pt atoms in the surface of these alloys has been modified slightly. With this understanding, we hope that electrocatalysts can begin to be designed on the basis of fundamental insight.
Catalysts
Detailed studies of the electrochemical oxygen reduction reaction (ORR) on catalyst materials are crucial to improving the performance of different electrochemical energy conversion and storage systems (e.g., fuel cells and batteries), as well as numerous chemical synthesis processes. In the effort to reduce the loading of expensive platinum group metal (PGM)-based catalysts for ORR in the electrochemical systems, many carbon-based catalysts have already shown promising results and numerous investigations on those catalysts are in progress. Most of these studies show the catalyst materials’ ORR performance as current density data obtained through the rotating disk electrode (RDE), rotating ring-disk electrode (RRDE) experiments taking cyclic voltammograms (CV) or linear sweep voltammograms (LSV) approaches. However, the provided descriptions or interpretations of those data curves are often ambiguous and recondite which can lead to an erroneous understanding of the ORR phenomenon in...
Journal of Applied Electrochemistry - J APPL ELECTROCHEM, 1998
A new method for electrochemical characterization of composite electrode materials is reported. A paste of the catalytic material in Nafion® is coated on a rotating ring disc electrode (RRDE) to partially simulate the working environment of a proton exchange membrane (PEM)/electrode composite as used in, for example, water electrolysis or PEM fuel cell operation. This allows direct comparison of a wide range of candidate electrocatalysts in a reproducible manner. Problems specific to these volumic electrodes are accommodated satisfactorily by rational modification of the standard expressions used in RRDE analysis. The value of the method is illustrated in studies of various cobalt complexes which show promise in dioxygen reduction; namely, cobalt tetramethoxyphenylporphyrin (CoTMPP), cobalt phthalocyanine (CoPC), and cobalt cyclam (CoCy), supported on a range of particulate carbons BP2000, Printex XE 2 and Vulcan XC-72. Typical electrochemical parameters have been measured or estima...