On the Origin of the OER Activity of Ultrathin Manganese Oxide Films

Abstract

There is an urgent need for cheap, stable, and abundant catalyst materials for photoelectrochemical water splitting. Manganese oxide is an interesting candidate as an oxygen evolution reaction (OER) catalyst, but the minimum thickness above which MnO x thin films become OER-active has not yet been established. In this work, ultrathin (<10 nm) manganese oxide films are grown on silicon by atomic layer deposition to study the origin of OER activity under alkaline conditions. We found that MnO x films thinner than 1.5 nm are not OER-active. X-ray photoelectron spectroscopy shows that this is due to electrostatic catalyst–support interactions that prevent the electrochemical oxidation of the manganese ions close to the interface with the support, while in thicker films, MnIII and MnIV oxide layers appear as OER-active catalysts after oxidation and electrochemical treatment. From our investigations, it can be concluded that one MnIII,IV–O monolayer is sufficient to establish oxygen evolution under alkaline conditions. The results of this study provide important new design criteria for ultrathin manganese oxide oxygen evolution catalysts.

Role of Electrode Thickness in NiFe Nanogranular Films for Oxygen Evolution Reaction

“…It is hence important to remark that an OER efficiency/mass loading correlation, as shown in Figure a–e, can be established only at a fixed nanostructure size and chemical composition as for SCBD films. In the case of incomplete control of such properties as a function of mass loading, the TOF behavior can be also affected implicitly by the nanograin/crystalline domain size or stoichiometry . It is the case of NiFeO synthesized by laser-assisted evaporation of ref , where the catalyst granular size has been shown to depend on the mass loading as well as on the substrate type.…”

“…32,33 Furthermore, this type of analysis is very limited for noble-metal-free electrodes. For MnO/Si 34 and LaSrMnO films, 35 a thickness analysis in the 1−27 nm range revealed the best OER efficiency for 4 nm thick films, while for NiFe hexacyanoferrate (0.5−10 mg/cm 2 range) a 5 mg/cm 2 has been identified as the ideal concentration. 36 For electrodeposited transition metal oxides, 37 the TOFs reported in the 0.1−100 μg/cm 2 density range show a high dependence on the oxide type, going from 10 s −1 for CoFeO to 0.001 s −1 for MnO.…”

“…The ECSA and the TOF were so far obtained for few noble/noble , or noble/non-noble − metal compounds, and usually the OER activity is solely discussed in terms of the loading of one of the two metals composing the nanoalloy as for Ir − or Ni. , Furthermore, this type of analysis is very limited for noble-metal-free electrodes. For MnO/Si and LaSrMnO films, a thickness analysis in the 1–27 nm range revealed the best OER efficiency for 4 nm thick films, while for NiFe hexacyanoferrate (0.5–10 mg/cm 2 range) a 5 mg/cm 2 has been identified as the ideal concentration . For electrodeposited transition metal oxides, the TOFs reported in the 0.1–100 μg/cm 2 density range show a high dependence on the oxide type, going from 10 s –1 for CoFeO to 0.001 s –1 for MnO.…”

ZnO–ZnFe2O4/Fe3O4/Carbon Nanocomposites for Ultrasensitive and Selective Dopamine Detection

“…Compared to ZF-CR-60/GCE, the peaks for Fe 2+ /Fe 3+ on ZF-60/Fe 3 O 4 /g-C/GCE are very prominent (Figure D). According to a recent study by Plate et al, the area under the oxidation peak (i.e., OP area ) correlates directly with the number of redox couples generated. The OP area value of Fe 2+ /Fe 3+ in ZnO–ZnFe 2 O 4 /Fe 3 O 4 /carbon is ∼10 times greater than that of ZnO–ZnFe 2 O 4 (Figure E), which means that a significant number of Fe 2+ /Fe 3+ ions are generated on the surface of ZF/Fe 3 O 4 /g-C/GCE.…”

Self-Supporting Metal-Organic Framework-Based Nanoarrays for Electrocatalysis

“…Earth-abundant transition metal oxides or hydroxides as one of the most promising candidates for OER have been extensively investigated due to their good cost-effectiveness and ease of preparation. − However, their catalytic performance is usually inhibited by the inherent poor conductivity, slow mass transport, and inadequate active sites. , In this regard, MOF used as a template or precursor to derive nanoarray-structured oxides or hydroxides can effectively relieve these issues and is extremely attractive for improving OER activity. − For example, Kong et al fabricated a 3D self-branching ZnCo 2 O 4 @N-doped carbon hollow nanowall arrays on carbon textiles (ZnCo 2 O 4 @NC/CTs) through controlled cation exchange and postannealing processes (Figure d) . The as-prepared ZnCo 2 O 4 @NC/CTs electrode exhibited favorable catalytic activity and OER kinetics (Figure e,f), which can be attributed to the following reasons.…”