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      Engineering Carbon Materials for Electrochemical Oxygen Reduction Reactions

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          Abstract

          The electrochemical oxygen reduction reaction (ORR) is the key energy conversion reaction involved in fuel cells, metal‐air batteries, and hydrogen peroxide production. Proliferation and improvement of the ORR requires wider use of new and existing high performance catalysts; unfortunately, most of these are still based on precious metals and become uneconomical in mass‐use applications. Recent progress suggests that low cost and durable carbon materials can potentially be developed as efficient ORR catalysts. Significant efforts have been made in discovering fundamental catalytic mechanisms and engineering techniques to guide and enable viable regulation of both the ORR activity and selectivity of these carbon catalysts. Starting from the fundamental understanding, this report reviews recent progress in engineering carbon materials from exotic chemical doping to intrinsic geometric defects for improved ORR. On the basis of both theoretical and experimental investigations reported so far in this area, future improvements in carbon catalysts are also discussed, providing useful pathways for more efficient and reliable energy conversion technologies.

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          Most cited references186

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          Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode

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            Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction.

            The large-scale practical application of fuel cells will be difficult to realize if the expensive platinum-based electrocatalysts for oxygen reduction reactions (ORRs) cannot be replaced by other efficient, low-cost, and stable electrodes. Here, we report that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells. In air-saturated 0.1 molar potassium hydroxide, we observed a steady-state output potential of -80 millivolts and a current density of 4.1 milliamps per square centimeter at -0.22 volts, compared with -85 millivolts and 1.1 milliamps per square centimeter at -0.20 volts for a platinum-carbon electrode. The incorporation of electron-accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four-electron pathway for the ORR on VA-NCNTs with a superb performance.
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              Anomalous increase in carbon capacitance at pore sizes less than 1 nanometer.

              Carbon supercapacitors, which are energy storage devices that use ion adsorption on the surface of highly porous materials to store charge, have numerous advantages over other power-source technologies, but could realize further gains if their electrodes were properly optimized. Studying the effect of the pore size on capacitance could potentially improve performance by maximizing the electrode surface area accessible to electrolyte ions, but until recently, no studies had addressed the lower size limit of accessible pores. Using carbide-derived carbon, we generated pores with average sizes from 0.6 to 2.25 nanometer and studied double-layer capacitance in an organic electrolyte. The results challenge the long-held axiom that pores smaller than the size of solvated electrolyte ions are incapable of contributing to charge storage.
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                Author and article information

                Contributors
                Journal
                Advanced Energy Materials
                Advanced Energy Materials
                Wiley
                1614-6832
                1614-6840
                August 2021
                July 14 2021
                August 2021
                : 11
                : 32
                Affiliations
                [1 ] ARC Centre of Excellence for Electromaterials Science Intelligent Polymer Research Institute Australia Institute for Innovative Materials (AIIM) Innovation Campus University of Wollongong Squires Way North Wollongong 2519 Australia
                [2 ] Center for Integrated Computational Materials Engineering School of Materials Science and Engineering Beihang University Beijing 100191 China
                [3 ] Department of Materials Science and Engineering University of Sheffield Sheffield S1 3JD UK
                Article
                10.1002/aenm.202100695
                4561d094-237b-465d-a053-a7218c2b5ce9
                © 2021

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