Redox

About: Redox is a research topic. Over the lifetime, 26853 publications have been published within this topic receiving 862368 citations. The topic is also known as: reduction-oxidation & reduction-oxidation reaction.

Catalytic mechanism of water oxidation with single-site ruthenium-heteropolytungstate complexes.

Abstract: Catalytic water oxidation to generate oxygen was achieved using all-inorganic mononuclear ruthenium complexes bearing Keggin-type lacunary heteropolytungstate, [RuIII(H2O)SiW11O39]5– (1) and [RuIII(H2O)GeW11O39]5– (2), as catalysts with (NH4)2[CeIV(NO3)6] (CAN) as a one-electron oxidant in water. The oxygen atoms of evolved oxygen come from water as confirmed by isotope-labeled experiments. Cyclic voltammetric measurements of 1 and 2 at various pH’s indicate that both complexes 1 and 2 exhibit three one-electron redox couples based on ruthenium center. The Pourbaix diagrams (plots of E1/2 vs pH) support that the Ru(III) complexes are oxidized to the Ru(V)–oxo complexes with CAN. The Ru(V)–oxo complex derived from 1 was detected by UV–visible absorption, EPR, and resonance Raman measurements in situ as an active species during the water oxidation reaction. This indicates that the Ru(V)–oxo complex is involved in the rate-determining step of the catalytic cycle of water oxidation. The overall catalytic mech...

An overview of electron acceptors in microbial fuel cells

Abstract: Microbial fuel cells (MFC) have recently received increasing attention due to their promising potential in sustainable wastewater treatment and contaminant removal. In general, contaminants can be removed either as an electron donor via microbial catalyzed oxidization at the anode or removed at the cathode as electron acceptors through reduction. Some contaminants can also function as electron mediators at the anode or cathode. While previous studies have done a thorough assessment of electron donors, cathodic electron acceptors and mediators have not been as well described. Oxygen is widely used as an electron acceptor due to its high oxidation potential and ready availability. Recent studies, however, have begun to assess the use of different electron acceptors because of the (1) diversity of redox potential, (2) needs of alternative and more efficient cathode reaction, and (3) expanding of MFC based technologies in different areas. The aim of this review was to evaluate the performance and applicability of various electron acceptors and mediators used in MFCs. This review also evaluated the corresponding performance, advantages and disadvantages, and future potential applications of select electron acceptors (e.g., nitrate, iron, copper, perchlorate) and mediators.

Oxidative degradation of organic compounds using zero-valent iron in the presence of natural organic matter serving as an electron shuttle.

Abstract: This study aims to understand the oxidative degradation of organic compounds utilizing zerovalent iron (ZVI) which is further promoted by the presence of natural organic matters (NOMs) (as humic acid (HA) or fulvic acid (FA)) working as electron shuttle mediators. The main target substrate used was 4-chlorophenol. Both HA and FA can mediate the electron transfer from the ZVI surface to O2, while enhancing the production of Fe2+ and H2O2 that subsequently initiates the OH radical-mediated oxidation of organic compoundsthrough Fenton reaction. The electron transfer-mediating role of NOMs was supported by the observation that higher concentrations of H2O2 and ferrous ion were generated in the presence of NOM. The NOM-induced enhancement in oxidation was observed with NOM concentrations ranging 0.1-10 ppm. Since the reactive sites responsible for the electron transfer action are likely to be the quinone moieties of NOMs, benzoquinone that was tested as a proxy of NOM also enhanced the oxidative degradation of 4-chlorophenol in the ZVI suspension. The NOM-mediated oxidation reaction on ZVI was completely inhibited in the presence of methanol, an OH radical scavenger, and in the absence of dissolved oxygen.

Investigating the Origin of Enhanced C2+ Selectivity in Oxide-/Hydroxide-derived Copper Electrodes during CO2 Electroreduction

Abstract: Oxide-/hydroxide-derived copper electrodes exhibit excellent selectivity toward C2+ products during the electrocatalytic CO2 reduction reaction (CO2RR). However, the origin of such enhanced selectivity remains controversial. Here, we prepared two Cu-based electrodes with mixed oxidation states, namely, HQ-Cu (containing Cu, Cu2O, CuO) and AN-Cu (containing Cu, Cu(OH)2). We extracted an ultrathin specimen from the electrodes using a focused ion beam to investigate the distribution and evolution of various Cu species by electron microscopy and electron energy loss spectroscopy. We found that at the steady stage of the CO2RR, the electrodes have all been reduced to Cu0, regardless of the initial states, suggesting that the high C2+ selectivities are not associated with specific oxidation states of Cu. We verified this conclusion by control experiments in which HQ-Cu and AN-Cu were pretreated to fully reduce oxides/hydroxides to Cu0, and the pretreated electrodes showed even higher C2+ selectivity compared with their unpretreated counterparts. We observed that the oxide/hydroxide crystals in HQ-Cu and AN-Cu were fragmented into nanosized irregular Cu grains under the applied negative potentials. Such a fragmentation process, which is the consequence of an oxidation-reduction cycle and does not occur in electropolished Cu, not only built an intricate network of grain boundaries but also exposed a variety of high-index facets. These two features greatly facilitated the C-C coupling, thus accounting for the enhanced C2+ selectivity. Our work demonstrates that the use of advanced characterization techniques enables investigating the structural and chemical states of electrodes in unprecedented detail to gain new insights into a widely studied system.