Electrochemical Synthesis of Layered Manganese Oxides Intercalated with Tetraalkylammonium Ions

Abstract

Thin films of birnessite-type layered manganese oxides with various interlayer spacings have been prepared on a platinum electrode by a one-step electrochemical procedure. The process involves a potentiostatic oxidation of aqueous Mn(2+) ions at around +1.0 V (Ag/AgCl) in the presence of tetraalkylammonium cations with different alkyl chain lengths. X-ray diffraction indicates that the films deposited with tetrabutylammonium (TBA), tetrapropylammonium (TPA), and tetraethylammonium (TEA) ions are composed of a single phase where unhydrated tetraalkylammonium ions are accommodated as a monolayer between manganese oxide layers. The interlayer spacing of the products increases in an order of TEA < TPA < TBA. The film deposited with tetramethylammonium (TMA) is a mixture of two phases relating to hydrated and unhydrated guest cations, the former being predominant probably as a result of less hydrophobic property of TMA compared to that of other tetraalkylammonium ions. The TBA(+)-intercalated Mn oxide film-coated electrode exhibits a good charge/discharge property in a KCl solution between 0 and +0.8 V. In this case, TBA(+) ions between the Mn oxide layers are rapidly replaced with K(+) in solution by ion exchange, accompanying a shrinkage of the interlayer. The incorporated K(+) ions as well as protons play an important role in the electrochemical conversion between Mn(4+) and Mn(3+) in the oxide layer. In the TBACl solution, the interlayer TBA(+) ions can be excluded electrochemically during the positive-going scan, concomitant with the oxidation of Mn(3+) sites. This causes an anodic current and the accompanying shrinkage of the interlayer. On the reverse scan, however, the compressed interlayer does not allow the incorporation of bulky TBA(+) ions from the electrolyte, with virtually no cathodic current observed. Such an obvious difference in electrochemical behavior between the two electrolytes can be recognized by considering that most of the Mn oxide surface is present inside the layered structure, not on the external surface. This indicates that the layered structure is formed over the entire film.

Liquid-phase aerobic oxidation of benzyl alcohol catalyzed by mechanochemically synthesized manganese oxide

“…Similar morphology has been observed for plate-like layered manganese oxide catalysts [22][23][24]; however, the larger surface area in these studies was probably caused by the presence of pillared material (e.g., alumina, lithium). The presence of pillared material creates a larger interlayer distance and results in pores having the form of parallel plates.…”

Mn-Mo-W Oxide Anodes for Oxygen Evolution in Seawater Electrolysis for Hydrogen Production

“…The peak binding energy (BE) values of Mn 2p 3=2 spectra are within 641.5-642.1 eV. According to literature reports, [24][25][26][27] cations with sufficient coverage to the IrO 2 substrate seems to be responsible for high oxygen evolution efficiency and high activity of the deposits during seawater electrolysis. Table 1 summarizes changes in composition, current efficiency of manganese deposition, thickness, grain size for oxide deposits and mass% of structural water with change in concentration and pH of the deposition electrolytes.…”

Removal of Methylene Blue from Aqueous Solution Using a Polarizable Nanolayered Manganese Oxide Film

“…The thus-prepared layered MnOx consists of negatively charged MnOx layers and Et4N cations sandwiched between them, as described in our previous paper. 5 The layered structure is substantially the same as those of alkylammonium/ MnOx materials prepared chemically by other researchers. 11,12 As shown in Fig.…”

“…4 The process involves an anodic oxidation of aqueous Mn 2+ ions in the presence of the corresponding guest cations. Our preliminary studies indicated that the bulky organic cations incorporated during electrodeposition are replaceable with smaller alkaline metal ions 5 or methylene blue 6 by ion-exchange. In the present study, the sorptive properties of layered manganese oxide film grown electrochemically toward methylene blue [MB, (CH3)2N(C6H3)-NS + (C6H3)N(CH3)2] were examined in detail in aqueous solutions with and without alkaline metal ions.…”

“…Layered manganese oxide contains Mn 3+ and Mn 4+ sites, and their ratio varies as a function of the electrode potential from 0 to +0.8 V without any change in the framework structure. 5 That is, negative charges on MnOx layers increase with an increase in the Mn 3+ content, and vice versa. Figure 6 shows time courses of the MB absorption taken in a solution containing MB alone at polarized potentials of 0 (a) and +0.8 (b) V. Unexpectedly, no significant change was observed between the reduced and oxidized states, despite apparently less negative charges being present on the MnOx sheets at +0.8 V. 5 This indicates that an electrostatic interaction is not necessarily required to uptake MB molecules.…”