Constructing Successive Active Sites for Metal‐free Electrocatalyst with Boosted Electrocatalytic Activities Toward Hydrogen Evolution and Oxygen Reduction Reactions
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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.Keywords:
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Developing a highly active and cost-effective cathode electrocatalyst with strong stability for oxygen reduction reaction (ORR) is extremely necessary. In this work, we reported a facile synthetic path to prepare a hybrid nanostructure formed of nitrogen-doped Ketjenblack carbon (N-KC) supported Co3O4 nanoparticles (Co3O4/N-KC), which could be used as a promising and stable electrocatalyst for ORR. Compared with the physical mixture of Co3O4 and N-KC and pure N-KC samples, the resulting Co3O4/N-KC nanohybrid afforded remarkably superb ORR activity with a half-wave potential of 0.82 V (vs. reversible hydrogen electrode, RHE) and a limiting current density of 5.70 mA cm-2 in KOH solution (0.1 M). Surprisingly, the Co3O4/N-KC sample possessed a similar electrocatalytic activity but better durability to the 20 wt% Pt/C catalyst. The remarkable ORR activity of the Co3O4/N-KC nanohybrid was mainly due to the strong coupling effect between Co3O4 and N-KC, the N species dopant, high electroconductivity, and the large BET surface area. Our work enlightens the exploitation of advanced Co3O4/carbon hybrid material alternative to the Pt-based electrocatalysts.
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Traditionally, ammonia (NH3 ) is synthesized via the Haber-Bosch process, which is not only commanded by harsh conditions but causes serious environmental pollution. Electrochemical reduction is recognized as a mild and environmentally benign alternative approach for NH3 synthesis, but an efficient electrocatalyst is a prerequisite for NH3 production. In this communication, the first experimental demonstration that Mn3 O4 nanocubes can be used as an efficient non-noble-metal electrocatalyst for N2 reduction reaction (NRR) at ambient conditions is reported. In 0.1 m Na2 SO4 aqueous solution, the catalyst delivers excellent NRR activity with an NH3 yield of 11.6 µg h-1 mg-1cat. and Faradaic efficiency of 3.0% at -0.8 V versus reversible hydrogen electrode. Notably, this catalyst also possesses satisfactory durability during the electrolysis and recycling test.
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This chapter contains sections titled: Introduction Five-membered systems with one heteroatom Five-membered systems with two heteroatoms Five-membered ring systems with more than two heteroatoms Six-membered heterocycles containing one heteroatom Six-membered heterocycles containing at least two heteroatoms Seven-membered heterocycles containing at least two heteroatoms: 1,4 and 1,5-benzodiazepines Polycyclic heterocycles Conclusion References
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Abstract Electrochemical carbon dioxide reduction reaction (CO 2 RR) provides a promising pathway for both decreasing atmospheric CO 2 concentration and producing valuable carbon‐based fuels. To explore efficient and cost‐effective catalysts for electrochemical CO 2 RR is of great importance, but remains challenging. Se‐doped carbon nanosheets (Se‐CNs) with a micro‐, meso‐, and macroporous structure are proposed for electrochemical CO 2 RR. Such an electrocatalyst combines the advantages of Se optimized active sites, hierarchical pores for facilitating reactant or ion penetration, transport and reaction, and large surface area for more accessible active sites. This Se‐CNs electrocatalyst exhibits over 11‐times enhanced partial current density of CO than the CNs without Se doping and high selectivity (90%) for CO 2 electroreduction to CO at a low potential of −0.6 V versus the reversible hydrogen electrode (vs RHE). Density function theoretical calculations reveal that the Se introduction in CNs lowers the free energy barrier of CO 2 RR and inhibits hydrogen evolution reaction effectively, thus improving the selectivity for CO 2 reduction to CO. This work presents a new member of the metal‐free electrocatalyst family, which is easily prepared, low cost, adjustable, and highly efficient for CO 2 RR.
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This chapter contains sections titled: Three-Membered Heterocycles with One Heteroatom Four-Membered Heterocycles with One Heteroatom Five-Membered Heterocycles with One Heteroatom Five-Membered Heterocycles with Two Heteroatoms Five-Membered Heterocycles with Three Heteroatoms Five-Membered Heterocycles with Four Heteroatoms Six-Membered Heterocycles with One Heteroatom Six-Membered Heterocycles with Two Heteroatoms Six-Membered Heterocycles with Three Heteroatoms Larger Heterocyclic and Polycyclic Ring Systems References
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