Ultrafine Mn₃O₄Nanowires/Three-Dimensional Graphene/Single-Walled Carbon Nanotube Composites: Superior Electrocatalysts for Oxygen Reduction and Enhanced Mg/Air Batteries

Abstract

The exploration of highly efficient catalysts for the oxygen reduction reaction to improve sluggish kinetics still remains a great challenge for advanced energy conversion and storage in metal/air batteries. In this work, ultrafine MnO nanowires/three-dimensional graphene/single-walled carbon nanotube catalysts with an electron transfer number of 3.95 (at 0.60 V vs Ag/AgCl) and kinetic current density of 21.7-28.8 mA cm were developed via a microwave-irradiation-assisted hexadecyl trimethylammonium bromide (CTAB) surfactant procedure to greatly enhance the overall catalytic performance in Mg/air batteries. To match the electrochemical activity of the cathode catalysts, a large-scale Mg anode prepared with micropersimmon-like particles via a mechanical disintegrator and Mg(NO)-NaNO-based electrolyte containing 1.0 wt % trihexyl(tetradecyl)phosphonium chloride ionic liquid were applied. Combining the ultrafine MnO nanowires/three-dimensional graphene/single-walled carbon nanotube as an efficient electrocatalyst for the oxygen reduction reaction and an Mg micro-/nanoscale anode in the novel electrolyte, the advanced Mg/air batteries demonstrated a high cell open circuit voltage (1.49 V), a high plateau voltage (1.34 V), and a long discharge time (4177 min) at 0.2 mA cm, showing a high energy density. Therefore, it is believed that this device configuration has great potential for application in new energy storage technologies.

Mechanisms of Two‐Electron versus Four‐Electron Reduction of Dioxygen Catalyzed by Earth‐Abundant Metal Complexes

“…nanotube catalysts exhibited ORR catalytic activity with the electron-transfer number of 3.95 and E 1/2 = À0.15 Vv s. Ag/AgCl in an O 2 -saturated 0.10 m KOH aqueous solution. [162] The ORR catalytic activity of Mn 3 O 4 nanowires/3D GN/SWCNT is higher than that of MnO 2 /reduced graphene oxide (MnO 2 /rGO) hybrid nanosheets. [163] The highest kinetic current density was observed for Mn 3 O 4 nanowires/3DG N/SWCNT composite, reaching 51.8 %o ft he Pt/C value.…”

“…In contrast to homogeneous manganese complex catalysts, which act as catalysts for two‐electron/two‐proton reduction of O 2 , ultrafine Mn 3 O 4 nanowires/three‐dimensional graphene/single‐walled carbon nanotube catalysts exhibited ORR catalytic activity with the electron‐transfer number of 3.95 and E 1/2 =−0.15 V vs. Ag/AgCl in an O 2 ‐saturated 0.10 m KOH aqueous solution . The ORR catalytic activity of Mn 3 O 4 nanowires/3D GN/SWCNT is higher than that of MnO 2 /reduced graphene oxide (MnO 2 /rGO) hybrid nanosheets .…”

“…The ORR catalytic activity of Mn 3 O 4 nanowires/3D GN/SWCNT is higher than that of MnO 2 /reduced graphene oxide (MnO 2 /rGO) hybrid nanosheets . The highest kinetic current density was observed for Mn 3 O 4 nanowires/3D GN/SWCNT composite, reaching 51.8 % of the Pt/C value …”

“…[163] The highest kinetic current density was observed for Mn 3 O 4 nanowires/3DG N/SWCNT composite, reaching 51.8 %o ft he Pt/C value. [162] Nickel complexes of thiophosphorylated calix [4]resorcinols exhibitedO RR catalytic activity in an O 2 -saturated 0.50 m H 2 SO 4 aqueous solutiona t0Vv s. Ag/AgNO 3 with n value of 2.1 (n: the number of electrons involved) in the ORR. [164] The Ni 3 (HITP) 2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) complex, which has ac onductive metal-organic framework (Figure 14), [165,166] also showede xcellent ORR catalytic activity in a0 .10 m KOH aqueouss olution at 0.767 Vv s. RHE with n = 2.25.…”

Electrocatalysis of Rechargeable Non‐Lithium Metal–Air Batteries

“…And during the charge process, MgO 2 would decompose first followed by more limited MgO decomposition. However, there are a few reports on bifunctional catalysts for Mg–air batteries in the past two years . Meanwhile, aluminum–/iron–air batteries are under the similar condition .…”