Tailoring Oxygen Reduction Reaction Pathway on Spinel Oxides via Surficial Geometrical‐Site Occupation Modification Driven by the Oxygen Evolution Reaction

Abstract

most valuable fundamental chemicals in various chemical industries, medical industries, and environmental remediation. [2] Interestingly, both these two focuses can be realized by the ORR process via different reaction routes or mechanisms. In detail, ORR with a complex multielectron process can proceed by two pathways, including the four-electron (4e − ) or two-electron 2e − ORR process to generate H 2 O or H 2 O 2 , respectively. [3] In the former pathway, oxygen is directly reduced to the final OHwhich is usually facilitated by platinum (Pt)based noble-metal electrocatalysts or some non-noble materials; while for the latter one, the first formed peroxide intermediateswill either diffuse away from the disk electrode or continues to be reduced to form OH − (H 2 O 2 + 2e − → 2OH − ), which is commonly occurred on the surface of carbonaceous materials or transition-metal oxides. [4] As illustrated, the mechanism for ORR is strongly affected by the surface structure, coordination environment, really exposed active centers, or crystal types of catalysts. [5] Among all the reported catalysts, typical mixed-metal cobalt manganese oxides (Mn x Co 3−x O 4±δ , 0 ≤ x ≤ 3, where δ indicates the oxygen non-stoichiometry) are usually deemed as promising catalysts in the oxygen electrochemical reaction, owing to high element abundance, considerable electro-activity, controllable tetrahedral and octahedral coordination, rich valence states. [6] Currently, various kinds of Mn-Co oxides have been reported for ORR; The oxygen reduction reaction (ORR) has been demonstrated as a critical technology for both energy conversion technologies and hydrogen peroxide intermediate production. Herein, an in situ oxygen evolution reaction (OER) surface evolution strategy is applied for changing the surface structure of MnCo 2 O 4 oxide with tetrahedral and octahedral cations vacancies to realize reaction pathway switching from 2e − ORR and 4e − ORR. Interestingly, the as-synthesized MnCo 2 O 4 -pristine (MnCo 2 O 4 -P) with the highest surficial Mn/Co octahedron occupation favors two electrons reaction routes exhibiting high H 2 O 2 selectivity (≈80% and reaches nearly 100% at 0.75 V vs RHE); after surface atoms reconstruction, MnCo 2 O 4 -activation (MnCo 2 O 4 -A) with the largest Mn/ Co tetrahedron occupation present excellent ORR performance through the four-electron pathway with an ultrahigh onset potential and half-wave potential of 0.78 and 0.92 V, ideal mass activity (MA), and turnover frequencies (TOF) values. Density functional theory (DFT) calculations reveal the concurrent modulations of both Co and Mn by the surface reconstructions, which improve the electroactivity of MnCo 2 O 4 -A toward the 4e − pathway. This work provides a new perspective to building correlation of OER activation-ORR property, bringing detailed understating for reaction route transformation, and thus guiding the development of certain electrocatalysts with specific purposes.

Heterogeneous interface catalysts with electron local exchange towards highly selective oxidation of biomass platform compounds

“…Delighted by the excellent performance of CoMn-MOCs-500, the reactivity of various biomass-derived furanic aldehydes was examined (Table 1). The substrates with strong electron-withdrawing groups 36 37,38 with corresponding FFT (shown in Supplementary Fig. 22), which confirm a well-defined partially inverse spinel structure of Co2MnO4 and a cubic spinel crystal structure of Co3O4, respectively.…”

MnOx Film-Coated NiFe-LDH Nanosheets on Ni Foam as Selective Oxygen Evolution Electrocatalysts for Alkaline Seawater Oxidation

“…35 The Mn 2p spectrum exhibits the spin−orbit doublet of Mn 2p 3/2 at 642.2 eV and Mn 2p 1/2 at 654.1 eV, with a spin energy separation of 11.9 eV, indicating the existence of the manganese oxide. 36,37 The Mn 2p 2/3 peak can further be deconvoluted into Mn 3+ and Mn 4+ sub-bands at 642.3 and 644 eV, respectively (Figure 2d). 38 The presence of the transition Mn oxidation states could be positive for the OER because the transition state would need a lower activation energy.…”

“…The change in binding energies of metallic cations implies that an electronic coupling interaction exists between the Mn species and NiFe-LDH, which can improve the intrinsic electrocatalytic activity of the catalyst . The Mn 2p spectrum exhibits the spin–orbit doublet of Mn 2p 3/2 at 642.2 eV and Mn 2p 1/2 at 654.1 eV, with a spin energy separation of 11.9 eV, indicating the existence of the manganese oxide. , The Mn 2p 2/3 peak can further be deconvoluted into Mn 3+ and Mn 4+ sub-bands at 642.3 and 644 eV, respectively (Figure d) . The presence of the transition Mn oxidation states could be positive for the OER because the transition state would need a lower activation energy .…”

Robust Oxygen Reduction Electrocatalysis Enabled by Platinum Rooted on Molybdenum Nitride Microrods

“…RRDE measurements (Figure 3d) indicate that the electron transfer number (n) was close to 4, and the H 2 O 2 yield was below 10% between 0.2 and 0.9 V vs RHE, suggesting an efficient four-electron reaction pathway (Figure 3e). 47,48 The catalytic stability of Pt/ Mo 2 N MRs was further examined by chronoamperometry. The i−t curves (Figure 3f) show that the current retention was 92.0% after 10,000 s for Pt/Mo 2 N MRs, much higher than that for Pt/C, signifying the significance of electronic interactions enabled by Mo 2 N MRs on Pt NPs.…”