In Situ Electrochemical Mn(III)/Mn(IV) Generation of Mn(II)O Electrocatalysts for High-Performance Oxygen Reduction

Abstract

Highlights MnO rich in oxygen vacancies has been synthesized. The synthesized MnO demonstrates excellent oxygen reduction reaction performance and high output power in Zn–air battery. The high catalytic activity is attributed to the synergetic catalytic effect between oxygen vacancies and in situ generated Mn 3+ /Mn 4+ . Abstract Among various earth-abundant and noble metal-free catalysts for oxygen reduction reaction (ORR), manganese-based oxides are promising candidates owing to the rich variety of manganese valence. Herein, an extremely facile method for the synthesis of cubic and orthorhombic phase coexisting Mn(II)O electrocatalyst as an efficient ORR catalyst was explored. The obtained MnO electrocatalyst with oxygen vacancies shows a significantly elevated ORR catalytic activity with a half-wave potential ( E 1/2 ) of as high as 0.895 V, in comparison with that of commercial Pt/C ( E 1/2 = 0.877 V). More impressively, the MnO electrocatalyst exhibits a marked activity enhancement after test under a constant applied potential for 1000 s thanks to the in situ generation and stable presence of high-valence manganese species (Mn 3+ and Mn 4+ ) during the electrochemical process, initiating a synergetic catalytic effect with oxygen vacancies, which is proved to largely accelerate the adsorption and reduction of O 2 molecules favoring the ORR activity elevation. Such an excellent ORR catalytic performance of this MnO electrocatalyst is applied in Zn–air battery, which shows an extra-high peak power density of 63.2 mW cm −2 in comparison with that (47.4 mW cm −2 ) of commercial Pt/C under identical test conditions. Electronic supplementary material The online version of this article (10.1007/s40820-020-00500-7) contains supplementary material, which is available to authorized users.

Tannin–Mn coordination polymer coated carbon quantum dots nanocomposite for fluorescence and magnetic resonance bimodal imaging

“…The high-resolution spectra of Mn 2p (Fig. 2c) present two peaks at 652.6 and 642.1 eV, which agreed with the spectra of Mn (2p1/2) and Mn (2p3/2) [37].…”

Rich Surface Oxygen Vacancies of MnO2 for Enhancing Electrocatalytic Oxygen Reduction and Oxygen Evolution Reactions

“…As shown in Figure 4a,b, a symmetric feature with g = 2.002 in ESR spectra was observed for all the MnO 2 samples, which was assigned to the unpaired electrons trapped at OVs. [ 19,38,39 ] Undoubtedly, the OVs were introduced on the surfaces of MnO 2 nanorods after the annealing process in air or H 2 atmosphere. The comparison in ESR signal intensity implied that more surface OVs were formed in the α‐MnO 2 and β‐MnO 2 prepared in H 2 than in that prepared in air.…”

“…Since the discovery of a cubane‐like Mn 3 O 4 Ca structure as active site in the natural oxygenic photosystem II (PS‐II), manganese oxides (MnO x ) as ORR and OER electrocatalysts have captured intensive attention due to their natural abundance, variety of crystallographic structures, low cost, and toxicity. [ 6,15-20 ] For example, manganese dioxide (MnO 2 ) can be formed in various crystal structures, such as α‐MnO 2 with 2 × 2 tunnels, γ‐MnO 2 with 1 × 2 tunnels, and β‐MnO 2 with 1 × 1 tunnels, which is a type of most commonly studied manganese oxides for supercapacitors and oxygen‐based electrochemical reactions. [ 6,15,18,21-25 ] More importantly, some manganese oxides exhibited considerable catalytic activity for both the ORR and OER, when with the noble metal catalysts, and had been identified as one of the most promising bifunctional candidates.…”

Strongly Coupled MnO2 Nanosheets/Silver Nanoparticles Hierarchical Spheres for Efficient Oxygen Reduction Reaction Electrocatalysis

“…For the Mn XPS spectra, Ag-MnO 2 -H-1.53 exhibits a negative shift in binding energy (0.39 eV) compared to MnO 2 -H, indicating an electronic effect between Mn and Ag, consistent with the SEM characterization. In addition, this decrease in binding energy of Mn 2p XPS spectra reveals an electron-rich state and weakened oxygen adsorption, benefiting the desorption of oxygenated intermediates during ORR . Moreover, MnO 2 -H displays Mn 3+ (641.9 eV), Mn 4+ (642.2 eV), Mn 5+ (643.3 eV), and satellite peaks (644.8 eV).…”