Electrochemical Oxygen Reduction to Hydrogen Peroxide via a Two‐Electron Transfer Pathway on Carbon‐Based Single‐Atom Catalysts
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Abstract Electrochemical reduction of oxygen is considered as a new strategy to achieve decentralized preparation of hydrogen peroxide (H 2 O 2 ) in a green manner. As a promising new type of catalytic material, carbon‐based single‐atom catalysts can achieve wide‐range adjustments of the electronic structure of the active metal centers while also maximize the utilization of metal atoms, toward electrochemical production of H 2 O 2 from the selective two‐electron transfer oxygen reduction reaction (ORR). Herein, starting from the reviewing of characterizing methods and reaction mechanisms of ORR via two‐electron and four‐electron transfer pathways, the vital role of binding strength between OOH intermediate and active sites in determining the activity and selectivity towards H 2 O 2 production is revealed and illustrated. Currently reported carbon‐based single‐atom catalysts for H 2 O 2 production are systematically summarized and critically reviewed. Moreover, with the underpinning chemistry to improve the overall efficiency, three aspects concerning the central metal atoms, coordinated atoms, and environmental atoms are comprehensively analyzed. Based on the understanding of the most current progresses, some predictions for future H 2 O 2 production via electrochemical routes are offered, which include catalyst designs at atomic levels, new synthesis strategies and characterization techniques, as well as interfacial superwetting interaction engineering at electrode and device levels.Keywords:
Carbon fibers
Abstract As well known, heteroatom doped carbon material served as metal‐free electrocatalyst for hydrogen evolution (HER) and oxygen reduction reactions (ORR) particularly relies on the heteroatom doping level. Here, we report a 3D porous nitrogen doped carbon (PNC) electrocatalyst with superior HER and ORR electrocatalytic activities derived from the calcination of the discarded cigarette butt and dicyandiamide possessing a high nitrogen content (20 at%). PNC electrocatalyst only demands 143 mV versus RHE to achieve 10 mA cm −2 ascribed to the high nitrogen percentile in PNC electrocatalyst favorable for constructing successive active centers contributing to efficiently catalyzing HER. Ignorable degradation in HER activity observed after 10000 potential cycles as well as undetectable decay in HER performance recorded after 12 h operation indicate high stability of PNC electrocatalyst. Meanwhile, half‐wave potential of PNC electrocatalyst reaches 0.81 V versus RHE in 1 M KOH electrolyte. Additionally, stable ORR activity attained after 1000 potential cycles is indicative of high stability. A comparably high zinc‐air battery performance with maximum power density of 66 mW cm −2 is achieved by PNC electrocatalyst. This study highlights the importance of nitrogen doping level in metal‐free electrocatalyst for boosting HER and ORR activities.
Heteroatom
Reversible hydrogen electrode
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Carbon fibers
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Electrocatalysis as a catalytic process involving oxidation or reduction through the direct transfer of electrons is of key importance subject in various fields of chemistry and associated sciences. Heterogeneous electrocatalysis is especially important to the development of water oxidation and fuel cells catalysts. This paper presents the brief description of the electrocatalysis and the mechanism of electrochemical reactions. Different factors and their influence on electrocatalytic activity, have been discussed. Role of nanoparticles in electrocatalysis received a particular emphasis. Long-term tasks of electrocatalysis were also definied.
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Metal-organic framework (MOF) based composite materials have attracted significant research interest in the electrocatalytic field. In this study, a carbonized polypyrrole coated MOF composite electrocatalyst ([email protected]) is developed, which is a nitrogen-modified MOF-based carbon used as non-precious oxygen reduction reaction (ORR) electrocatalyst. Physical characterizations prove that the [email protected] electrocatalyst has high nitrogen doping (2.53 at.%) and effective graphite and pyridinium nitrogen doping (86.6%). When compared with commercial Pt/C, as-obtained [email protected] electrocatalyst shows good ORR performance (∆E1/2 = −22 mV) with good stability (87.8%) and methanol tolerance. All results indicate that MOF-based [email protected] electrocatalyst is an effective and promising electrocatalyst for ORR.
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La 0.6 Ca 0.4 CoO 3 perovskite electrocatalyst had been synthesized by organic acid-aided method. The impact of the cal-cining conditions on the electrocatalyst preparation was studied by XRD, TEM and optimal results were given. The perfor-mance of bifunctional oxygen electrode electrocatalyst was evaluated preliminarily by galvanostatic polarization curve method. The results show that the electrocatalyst synthesized at 700 ℃for 2h has the characteristics of single phase, single crystal and smaller grain size, so the condition is optimal for preparing the electrocatalyst. The electrocatalyst made under that condition has better bifunctional oxygen electrode electrocatalytic activity and stability, which is promising as bifunctional oxygen elec-trode electrocatalyst for the MH-Air secondary battery application.
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Oxygen evolution
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Abstract We describe a facile method to enhance the CO tolerance of a fuel‐cell electrocatalyst dramatically based on carbon nanotubes. The electrocatalyst is composed of Pt deposited on carbon nanotubes wrapped in poly[2,2′‐(2,6‐pyridine)‐5,5′‐bibenzimidazole] (PyPBI) further covered by poly(vinylpyrrolidone) (PVP) through multipoint hydrogen bonding interactions between the PyPBI and PVP. The PVP‐coated electrocatalyst showed a ∼10 times higher CO tolerance compared to the non‐PVP‐coated electrocatalyst under a high (4 m ) methanol concentration. Additionally, the PVP‐coated electrocatalyst showed an enhancement in the Pt stability because of the stabilization of the Pt‐NP by the PyPBI and PVP. After the durability test, the PVP‐coated electrocatalyst still showed ∼8 times higher CO tolerance because of the presence of the PVP bound stably with PyPBI. This study provides useful information for the design and fabrication of a state‐of‐the‐art anodic electrocatalyst for direct methanol fuel cells.
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Chemisorption
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