A metal-free bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions

Abstract

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are traditionally carried out with noble metals (such as Pt) and metal oxides (such as RuO₂ and MnO₂) as catalysts, respectively. However, these metal-based catalysts often suffer from multiple disadvantages, including high cost, low selectivity, poor stability and detrimental environmental effects. Here, we describe a mesoporous carbon foam co-doped with nitrogen and phosphorus that has a large surface area of ∼1,663 m(2) g(-1) and good electrocatalytic properties for both ORR and OER. This material was fabricated using a scalable, one-step process involving the pyrolysis of a polyaniline aerogel synthesized in the presence of phytic acid. We then tested the suitability of this N,P-doped carbon foam as an air electrode for primary and rechargeable Zn-air batteries. Primary batteries demonstrated an open-circuit potential of 1.48 V, a specific capacity of 735 mAh gZn(-1) (corresponding to an energy density of 835 Wh kgZn(-1)), a peak power density of 55 mW cm(-2), and stable operation for 240 h after mechanical recharging. Two-electrode rechargeable batteries could be cycled stably for 180 cycles at 2 mA cm(-2). We also examine the activity of our carbon foam for both OER and ORR independently, in a three-electrode configuration, and discuss ways in which the Zn-air battery can be further improved. Finally, our density functional theory calculations reveal that the N,P co-doping and graphene edge effects are essential for the bifunctional electrocatalytic activity of our material.

B, N Codoped and Defect‐Rich Nanocarbon Material as a Metal‐Free Bifunctional Electrocatalyst for Oxygen Reduction and Evolution Reactions

“…High‐resolution XPS spectra are collected to further explore the bonding configuration, and the results are presented in Figure 2B,C and Table S1 (Supporting Information). The N 1s peak for N‐carbon can be deconvoluted into four contributions, that is, N1 (398.3 eV), N2 (399.9 eV), N3 (401.4 eV), and N4 (404.1 eV), which correspond to the pyridinic N, pyrrolic N, graphitic N, and oxidized N groups 12, 17, 39, 40, 41. A new peak observed at 397.6 eV for B,N‐carbon can be attributed to the N—B bond 42, 43.…”

“…Since then, heteroatom dopants, such as N,9, 12, 13 B,14, 15 P,16, 17 and S,18, 19, 20 have been widely incorporated into nanocarbon materials to improve their electrocatalytic activities. The inherent differences in the electronegativity and atomic size between carbon and these heteroatoms could modify the inherent electronic structures of nanocarbon materials, thereby creating new catalytic sites and facilitating the chemisorption/desorption of intermediates and thus enhancing the catalytic activities 9, 13, 14, 17, 21, 22. In addition to heteroatom dopants, the intrinsic carbon defects, such as topological (pentagonal, heptagonal, etc.)…”

Advanced Architectures and Relatives of Air Electrodes in Zn–Air Batteries

“…For example, primary battery assembled by N,P co‐doped carbon foam demonstrated an open‐circuit potential of 1.48 V and energy density of 835 Wh kg Zn −1 ( Figure 7 a,b) 188. When assembled to rechargeable batteries in the form of tri‐electrode configuration, the cell demonstrated an excellent stability of 600 charge/discharge cycles for 100 h (Figure 7d), which was almost equal to that of Pt/C and RuO 2 in tri‐electrode and better than same carbon electrocatalyst in the two‐electrode configuration of 180 cycles at 2 mA cm −2 (Figure 7c).…”

“…Cycling performance of rechargeable Zn–air batteries corresponding two‐electrode configuration (c), and trielectrode configuration (d) at current density of 2 mA cm −2 . Reproduced with permission 188. Copyright 2015, Nature.…”

A Bifunctional Electrocatalyst for Oxygen Evolution and Oxygen Reduction Reactions in Water

“…Hence, there is a strong motivation to develop catalysts that can oxidize water efficiently under ambient conditions. The development of efficient bifunctional catalysts has been a fast evolving area 15. Although there are some reports of bifunctional catalysts for the reversible conversion of protons into H 2 , reports on nonprecious metal based electrocatalysts which can efficiently oxidize water to oxygen and also reduce oxygen are rare.…”