Optimization of Catalytic Sites in Cobalt‐Modified Nitrogen‐Doped Carbon towards High‐Performance Oxygen Reduction Electrocatalysts for Zinc‐Air Batteries

Abstract

Efficient yet low-cost electrocatalysts for the oxygen reduction reaction (ORR) are highly desirable for energy systems such as metal-air batteries and fuel cells. Herein, we report the synthesis of efficient cobalt-modified nitrogen-doped carbon (NÀ C/Co) electrocatalysts by using a one-pot pyrolysis. The abundant source of N in g-C 3 N 4 contributes to the in situ N doping in the carbon matrix, which favors the formation of Co-related catalytic active sites. The NÀ C/Co-1 (prepared with 1 mmol Co salt) sample exhibits the best performance towards the ORR, with a positive half-wave potential of 0.86 V (vs. the reversible hydrogen electrode, RHE), high stability and excellent methanol tolerance, which outperforms the commercial Pt/C catalyst. We find that the high performance is dependent on the optimal content of Co that can achieve the maximum amount of CoÀ N x catalytic species. In addition, we reveal that the size effect of Co nanoparticles is not the determining factor for the ORR activity in the current system, as the kinetics of the ORR reaction is dominantly determined by the active sites derived from CoÀ N x species. By exploiting the NÀ C/Co-1 sample as an air cathode catalyst, the assembled Zn-air battery presents a maximal power density of 153 mW cm À 2 as well as good durability during continuous cycle tests.

Engineering Active Sites in Three‐Dimensional Hierarchically Porous Graphene‐Like Carbon with Co and N‐Doped Carbon for High‐Performance Zinc‐Air Battery

“…As a bifunctional ORR/OER electrocatalyst, Co-NC/3DHPGC exhibits a ΔE value of 0.78 V (Figure 4c), which is not only lower than that of all the other electrocatalysts (ΔE Co/3DHPGC = 0.95 V, ΔE Pt/C = 0.97 V, and ΔE RuO2 = 1.24 V) tested here but also comparable to or even lower than that of the most active Co-NC-based bifunctional electrocatalysts reported so far in the literature (Table S1). The excellent bifunctional oxygen electrocatalytic activity of Co-NC/ 3DHPGC can be ascribed to several factors: 1) formation of Co-NC active sites, which are known as highly active for ORR; [12][13][14][15][16][17][18][19][20][21][22][23][24] 2) accessibility of active sites through mesopores of 3DHPGC and thin layer of NC; [27,41] and 3) formation of graphitic carbon layer on Co, which facilitates electron transfer at interface. [10]…”

“…[7,11] Recent studies reveal that the coupling of Co nanoparticles with heteroatom doped carbon, especially, N-doped carbon (NC) materials can, because of the improved electron transfer at the interface between Co and NC, lead to satisfactory ORR and OER in terms of both high positive onset potential and high current density. [6,7,10,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] However, most synthesis methods of Co-NCbased catalysts involve the uncontrolled pyrolysis of metalorganic framework, which results in low surface area and nonhomogeneous distribution of active sites, thereby decreasing the active sites accessibility in electrocatalysis. Therefore, to accelerate the overall kinetics of oxygen electrocatalysis, it is necessary to design a high-performance Co-NC-based electrocatalyst by nanoengineering of the surface of the catalyst with metallic Co and non-metallic N, controlled interface layer construction, and surface area enhancement, which can maximize the accessibility of the active sites.…”

“…Therefore, to accelerate the overall kinetics of oxygen electrocatalysis, it is necessary to design a high-performance Co-NC-based electrocatalyst by nanoengineering of the surface of the catalyst with metallic Co and non-metallic N, controlled interface layer construction, and surface area enhancement, which can maximize the accessibility of the active sites. [16,29,30] However, the exact configuration of the active sites of Co-NC-based electrocatalysts is still under debate and challenges remain in the development of high-performance Co-NC-based catalysts due to poor active site accessibility.…”

Potassium‐Ion Activating Formation of Fe−N−C Moiety as Efficient Oxygen Electrocatalyst for Zn‐Air Batteries

“…[1] However, a prompt increase in the energy demand because of industrialization and motorization and the associated environmental problems lead to the requisite for replacing traditional fuels with sustainable clean energy sources. [2][3][4][5][6][7][8][9][10] In this regard, the best alternatives are fuel cells and metal air batteries having zero emission and high energy conversion rate. [11][12][13][14] Among them, the oxygen reduction reaction (ORR) at cathode is of utmost importance due to the sluggish kinetics, limiting their practical applications.…”

“…Presently, about 78 % of the global energy requirement is accomplished by using fossil fuels [1] . However, a prompt increase in the energy demand because of industrialization and motorization and the associated environmental problems lead to the requisite for replacing traditional fuels with sustainable clean energy sources [2–10] . In this regard, the best alternatives are fuel cells and metal air batteries having zero emission and high energy conversion rate [11–14] .…”