MnN₄ Oxygen Reduction Electrocatalyst: Operando Investigation of Active Sites and High Performance in Zinc–Air Battery

Abstract

The development of inexpensive and highly efficient nonprecious metal catalysts to substitute Pt in the alkaline oxygen reduction reaction is an appealing idea in the energy field. Herein, a Mn oxygen reduction electrocatalyst with a half‐wave potential (E1/2) as high as 0.910 V under an alkaline oxygen reduction reaction process is developed, and the dynamic atomic structure change of the highly efficient Mn single‐atomic site is investigated using operando X‐ray absorption spectroscopy. These results demonstrate that the low‐valence MnL+N4 is the active site during the oxygen reduction process. Density functional theory reveals that facile electron transfer from MnL+N4 to adsorbed *OH species plays a key role in the excellent electrocatalytic performance. Moreover, when assembled as the cathode in a zinc–air battery, this MnN4 material shows high power density and excellent durability, demonstrating its promising potential to substitute the Pt catalyst in practical devices.

Recent Advances on MOF Derivatives for Non-Noble Metal Oxygen Electrocatalysts in Zinc-Air Batteries

“…The electrochemical tests showed that the Mn-based SACs had an excellent performance on ORR showing promising half-wave potential of 0.87 V and diffusion current-limiting performance of ZABs under alkaline conditions, which was superior to most Mn-based nanomaterial catalysts and Pt/C catalysts. More recently, well-dispersed Mn single-atoms anchored nitrogen-doped carbon with Mn–N 4 configuration catalyst (Mn-SAS/CN) was prepared by one-step thermal activation of Mn(CH 3 COO) 2 @ZIF-8 precursor [ 114 ]. The operando X-ray absorption spectroscopy analysis showed that the active sites of Mn changed with the applied potential under the basic ORR condition, and Mn L+ –N 4 without covering OH ads was the catalytic center.…”

Inhibiting Surface Diffusion to Synthesize 3D Bicontinuous Nanoporous N‐Doped Carbon for Boosting Oxygen Reduction Reaction in Flexible All‐Solid‐State Al‐Air Batteries

“…The residual Mn was verified to be not the major ORR active sites by the SCN − poisoning experiment (Figure S12, Supporting Information). [ 31 ] In addition, the effect of pyrolysis time on the structure and ORR performance of N‐NPC‐900 sample was also investigated (Figure S13, Supporting Information). The ORR catalytic activity of N‐NPC samples was analyzed by double‐layer capacitance ( C dl ) values, electrochemical impedance spectroscopy (EIS), and N‐dopant concentrations.…”

Engineering Single Atom Catalysts to Tune Properties for Electrochemical Reduction and Evolution Reactions

“…Han et al [ 28 ] developed Mn Single Atom Site catalysts on N‐doped Carbon supports (Mn‐SAS/CN) via single stage pyrolysis, yielding NPs with dodecahedral morphologies (Figure 8e). EDX mappings in Figure 8f illustrate uniform Mn (green), C (blue), and N (red) distributions over whole Mn‐SAS/CN surfaces, while AC HAADF‐STEM confirm Mn isolation via circled (red) bright dots (Figure 8g).…”

“…Further, Han et al [ 28 ] studied the active sites of Mn‐N 4 for oxygen reduction. More directly, dynamic and reversible modulation of Mn active center valences from higher (Mn H+ ‐N 4 ) to lower (Mn L+ ‐N 4 ) charges can responsively tune OH coverage in ORR and related reactions.…”

“…With regard to overcoming such technological limitations, single‐atom catalysts (SACs) are highly promising, featuring active and isolated single metal atoms stabilized by supportive substrates or alloying. [ 24–29 ] SACs are distinguished from nanoparticle (NP) catalysts through their lack of metal–metal bonds, usually yielding positively charged single metal atoms. Unique SAC geometric and electronic properties significantly alter reactant, intermediate, and product interactions, enhancing reaction activity to assist refined chemical manufacturing.…”