Tuning Co‐Catalytic Sites in Hierarchical Porous N‐Doped Carbon for High‐Performance Rechargeable and Flexible Zn‐Air Battery

Abstract

Although noble metal-based materials are known as favorable catalysts for electrocatalytic oxygen reduction, their scarcity and expensive prices are unsatisfactory. Hence, developing earth-abundant and efficient bifunctional oxygen electrocatalysts for rechargeable ZABs is demanded and remains grand challenging.Carbon materials with unique surface properties and high structural flexibility have been used to prepare advanced electrocatalysts by heteroatom doing and/or loading of various transition metals from nanoparticles to single atoms. [3] Currently, the strategy to improve the electrocatalytic activity of bifunctional ORR/OER electrocatalysts is proposed by the synergistic effect via the integration of multiple active components. Alternatively, the modulation of the geometric and porous structure would facilitate mass transfer and enhance the number of accessible active sites. Obviously, the uniform loading of additional metal active sites is of importance in improving electrocatalytic activity. [4] Specifically, the cobalt species were anchored on the conductive carbon supports via the thermal treatment of organic precursors with the good capability to disperse metal species (such as ZIF-67). [5,6] However, the sintering and aggregation of cobalt species during the annealing process would result in poor electrocatalytic performance. Alternatively, molecular assembly is an efficient strategy for preparing the controllable architectures of catalysts. [7] Therefore, it is highly desirable to integrate the wellshaped 3D porous carbons with cobalt active sites for high-performing electrocatalysis.Inspired by the affinity of receptors and ligands for directly targeting cancer cells, the mini biomimetic coordination of chitosan and folic acid (FA) provides a reaction platform to facilitate the anchoring of metal ions. Herein, the pre-coordination of chitosan with folic acid led to the formation of hierarchical aggregates composed of nanosheets. Their surface functional groups (e.g., carboxylic groups, amino groups) provide the anchoring sites for metal ions via the metal-nitrogen coordination and can avoid the agglomeration of excessive metal ions. During the carbonization, the presence of cobalt species promotes the selfcatalytic growth of carbon nanotubes on the carbon nanosheets of 3D hierarchical porous nanoflowers (CoCNTs/PNAs). With a low boiling point of 732 °C, the thermal release of ZnCl 2The strategy of heteroatom doping and metal active sites can synergistically promote oxygen electrocatalysis. Especially, the combination of theoretical simulations with experimental results provides new opportunities to understand the electrocatalytic mechanism. Herein, the 3D carbon nanosheets aggregate with highly branched carbon nanotubes and cobalt active sites (CoCNTs/PNAs) is prepared via the facile self-assembly-pyrolysis strategy. The CoCNTs/PNAs electrocatalysts exhibit superior bifunctional activities to oxygen reduction (E 1/2 = 0.925 V) and evolution (E j = 10 = 1.54 V) reactions, surpassing those of Pt/C-...

High-dispersion Co/N/C ultra-thin carbon nanosheets modified with trace Ce as efficient oxygen reduction reaction catalysts

“…[51][52][53] The Co-N chemical bond is regarded as one of the most efficient active sites in electrocatalytic reaction. [54][55][56] As shown in Table S3 (ESI †), Ce-Co/N/C has a larger Co-N bond content (18.16%) than Co/N/C (11.94%). The results indicated that there were more Co-N active sites in Ce-Co/N/C which affected the reaction rate.…”

Research progress on the construction of synergistic electrocatalytic ORR/OER self-supporting cathodes for zinc–air batteries

“…10d-f). 188 4.4.3 Adsorption energy and differential charge density. The adsorption energy of oxygen is an important criterion to conclude the oxygen reaction activity.…”

Carbon-based single-atom catalysts: impacts of atomic coordination on the oxygen reduction reaction

“…to nitrogen-doped carbon is an efficient way to increase ORR activity. [107][108][109][110][111][112][113] For the carbon-based transition metal catalysts, it is obvious that the transition metal is essential to the functioning of the active center, but the exact active center remains undetermined and controversial, and the M-N x component is the active site for catalytic ORR, according to the more widely accepted theory. In addition the differences caused by the inherent nature of the coordination engineering of the N and C atoms controls the electrical structure of the catalytic core more so than the metal atoms themselves.…”