Controlled deposition of size-selected MnO nanoparticle thin films for water splitting applications: reduction of onset potential with particle size

Abstract

Emulating water oxidation catalyzed by the oxomanganese clusters in the photosynthetic apparatus of plants has been a long-standing scientific challenge. The use of manganese oxide films has been explored, but while they may be catalytically active on the surface, their poor conductivity hinders their overall performance. We have approached this problem by using manganese oxide nanoparticles with sizes of 4, 6 and 8 nm, produced in a sputter-gas-aggregation source and soft-landed onto conducting electrodes. The mass loading of these catalytic particles was kept constant and corresponded to 45%-80% of a monolayer coverage. Measurements of the water oxidation threshold revealed that the onset potential decreases significantly with decreasing particle size. The final stoichiometry of the catalytically active nanoparticles, after exposure to air, was identified as predominantly MnO. The ability of such a sub-monolayer film to lower the reaction threshold implies that the key role is played by intrinsic size effects, i.e., by changes in the electronic properties and surface fields of the nanoparticles with decreasing size. We anticipate that this work will serve to bridge the knowledge gap between bulk thick film electrocatalysts and natural photosynthetic molecular-cluster complexes.

Biogenic and Synthetic MnO2 Nanoparticles: Size and Growth Probed with Absorption and Raman Spectroscopies and Dynamic Light Scattering

“…Consequently, biogenic oxides are good candidates for clean water technologies for treating organic and inorganic pollutants. Additionally, there is interest in exploiting them as catalysts in photoelectrochemical water splitting − and in energy storage systems. − As with many metal oxides, the properties and potential applications of MnO 2 , including bacterial MnO 2 from water oxidation to toxic metal sequestrationare influenced strongly by the particle size, which, in turn, determines the surface area and the density of highly reactive surface and edge sites. − …”

Suppressing the Unfavorable Surface Layer Growth on Na0.44MnO2 Cathode by a NaTi2(PO4)3 Coating To Improve Cycling Stability and Ultrahigh Rate Capability

“…To explain the special island-like outgrowth, we propose a formation mechanism (Figure f). During the cycling, due to the presence of oxidizing Mn 4+ in the Na 0.44– x MnO 2 and the good catalytic activity of MnO x , , the cathode–electrolyte interfacial reactions occur on the surface of the Na 0.44 MnO 2 particles, which results in the production of ROCONa and the manganese compounds. Because ROCONa contains organic functional groups, its polarity is low, which suggests some hydrophobic characteristic.…”

Electrical and Optical Characteristics of Copper Antimony Sulphide Thin Films Fabricated in Chemical Baths of Different Growth Media

“…The method relies on the fact that, without application of external fields, thin film (TF) can be grown on both metallic and non metallic substrates by dipping them into a suitable reaction baths that contain metallic salts and in a growth medium of either deionised water or polyvinyl alcohol (PVA). Extensive literature on size reduction effect is available [6][7][8][9]. CBD technique as well as some other techniques have been used to improve various chalcogenides, especially sulphides from the early binary TFs to the present frontier of ternary, quaternary and multinary devices, such as copper indium sulphide, that possess band gaps appropriate for solar light harvesting, photovoltaic properties, selective surfaces and other optoelectronic properties [10].…”