Preferentially Engineering FeN₄ Edge Sites onto Graphitic Nanosheets for Highly Active and Durable Oxygen Electrocatalysis in Rechargeable Zn–Air Batteries

Abstract

conversion system due to their high energy density, low cost, and zero emission. [3-6] However, the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during the charge and discharge process result in high overpotential and low specific energy, thereby impeding the commercialization of Zn-air batteries. [7-12] Motivated by this challenge, great endeavors have been paid to exploit oxygen electrocatalysts with accelerated kinetics, with noble-metalbased materials known as the mainstream catalysts (Pt for ORR, Ir and Ru for OER). These catalysts, however, are only function actively to one of the two essential reactions, behave inactively to the other, and are criticized for their expensive and scarce nature. Therefore, developing costeffective and efficient bifunctional oxygen electrocatalysts is regarded a cutting edge and essential research topic. [13-16] The emergence of single-atom catalysts (SACs) is bringing out new opportunities to oxygen electrocatalysis. SACs based M-N-C with varied metal centers (M represents Fe, Co, Cu, Mn, Ni, Zn, etc.) have been explored as oxygen electrocatalysts. [17-24] Among them, single-atom Fe-N-C catalysts with FeN 4 Single-atom FeN 4 sites at the edges of carbon substrates are considered more active for oxygen electrocatalysis than those in plane; however, the conventional high-temperature pyrolysis process does not allow for precisely engineering the location of the active site down to atomic level. Enlightened by theoretical prediction, herein, a self-sacrificed templating approach is developed to obtain edge-enriched FeN 4 sites integrated in the highly graphitic nanosheet architecture. The in situ formed Fe clusters are intentionally introduced to catalyze the growth of graphitic carbon, induce porous structure formation, and most importantly, facilitate the preferential anchoring of FeN 4 to its close approximation. Due to these attributes, the as-resulted catalyst (denoted as Fe/N-G-SAC) demonstrates unprecedented catalytic activity and stability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) by showing an impressive half-wave potential of 0.89 V for the ORR and a small overpotential of 370 mV at 10 mA cm −2 for the OER. Moreover, the Fe/N-G-SAC cathode displays encouraging performance in a rechargeable Zn-air battery prototype with a low charge-discharge voltage gap of 0.78 V and long-term cyclability for over 240 cycles, outperforming the noble metal benchmarks.

Engineering local coordination environments and site densities for high‐performance Fe‐N‐C oxygen reduction reaction electrocatalysis

“…Further studies indicated that the edge‐hosted FeN 4 sites were more likely to be formed on the margin of the pores in the carbon matrix (Figure 3C). 40–43 DFT calculations also added further evidence for the high activity of edge‐hosted FeN 4 sites 41 . As shown in Figure 3C, the binding of O 2 * and OOH* was endothermic on the bulk‐hosted FeN 4 model (Figure 3D), While all steps were exothermic and downhill on the other three edge‐hosted FeN 4 models.…”

N, S Codoped Carbon Matrix‐Encapsulated Co9S8 Nanoparticles as a Highly Efficient and Durable Bifunctional Oxygen Redox Electrocatalyst for Rechargeable Zn–Air Batteries

“…Furthermore, a wide range of comparisons shows that the as‐prepared Co 9 S 8 @N, S–C catalyst is better than most of the highly performing bifunctional catalysts reported so far (see Table S1 in the Supporting Information for a detailed comparison). [ 10,27–49 ]…”

“…Furthermore, a wide range of comparisons shows that the as-prepared Co 9 S 8 @N, S-C catalyst is better than most of the highly performing bifunctional catalysts reported so far (see Table S1 in the Supporting Information for a detailed comparison). [10, In order to verify the role of Co 9 S 8 in the catalytic activity of Co 9 S 8 @N, S-C catalyst, the removal experiment of Co 9 S 8 nanoparticles test was carried out. After the Co 9 S 8 @N, S-C catalyst was ball milled and acid leached at 80 °C with 0.5 m H 2 SO 4 for 12 h, we got its XRD spectrum shown in Figure S13 in the Supporting Information, in which it can be seen that the characteristic peaks of Co 9 S 8 become very weak, indicating that most of the Co 9 S 8 have been removed by the process.…”

“…[ 8 ] Among them, experimental and theoretical studies have shown that transition metal sulfides and phosphates have better OER activity, but lack of ORR activity, [ 9 ] and transition metal iron nitrogen–carbon (Fe–N–C) materials are the most excellent ORR catalysts. [ 10 ] Unfortunately, for Fe–N–C materials, the Fenton reaction of Fe center and byproduct H 2 O 2 of ORR will produce hydroxyl and oxygen radicals, which will not only change the chemical structure of the catalyst and affect the durability of the catalyst, but also corrode the ion membrane and destroy the battery device. [ 11 ] In addition, studies have also shown that the performance of iron‐based catalysts in OER cannot surpass other 3d transition metals (such as Co and Ni).…”

Research Progress of Carbon-Supported Metal Single Atom Catalysts for Oxygen Reduction Reaction

“…9 [74] Ma 等 [73] [75] Fig. 10 Formation process and Structural characterizations of Mn-N2C2 [75] (a) Illustration of the formation of MnSAC, (b, c) HAADF-STEM images of MnSAC, (d) iR-corrected ORR polarization curves for MnSAC, CN, and 20% Pt/C, (e) Mn K-edge XANES and (f) FT EXAFS spectra of MnSAC and the references,(g) Atomic structure model for MnSAC Shang 等 [75] [80][81][82] 、 析氢反应(HER) [83][84][85] 、CO2 还原 [86][87][88][89][90] 、电还原合成氨 (NRR) [50,[91][92][93] 、硝酸盐还原反应(NO3-RR) [94] 以及其 它有机反应 [95][96] 等均显示出优秀的催化活性。 在电化学方面，SACs 可用作电极催化剂，提高 电化学储能装置的应用性能。以 SACs 作为正极的 质子交换膜燃料电池显示出优秀的功率密度 [97][98] 。 引入 SACs 的金属-空气电池展示出高开路电压以及 优秀的稳定性 [99][100][101][102][103][104][105] 。另外，SACs 还能够应用于锂 硫电池 [106][107] 、CO2 电池 [90] 以及染料敏化太阳能电 池 [108][109]…”