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Iron porphyrins are synthesized by systematically introducing electron withdrawing groups (EWGs) on pyrroles to evaluate the relationship between rate (k) and overpotential (η). The results indicate that while EWGs lead to a rise in the thermodynamic FeIII/II reduction potential (E0), the potential of O2 reduction reaction (ORR) does not scale with E0. More importantly, the iron porphyrins with higher E0 shows an order of magnitude higher rate of ORR than unsubstituted iron tetraphenyl porphyrin. This contests the scaling relationship often offered to predict rates of ORR by iron porphyrins based on their E0. Mechanistic investigations reveal that the rate determining steps of ORR changes between these iron porphyrins with EWG’s as the pKa and E0 of several key intermediate species have likely changed on altering the macrocycle. These results suggests that linear dependence of log(rate) on E0 or η may only be valid for complexes where the rds of ORR remains the same.

The development of electrocatalysts for the selective O2-to-H2O conversion, the O2 reduction reaction (ORR), is of great interest for improving the performance of fuel cells. In this context, molec...

Photocatalysts with the photocatalytic “memory” effect could resolve the intrinsic activity loss of traditional photocatalysts when the light illumination is turned off. Due to the dual requirements of light absorption and energy storage/release functions, most previously reported photocatalysts with the photocatalytic “memory” effect were composite photocatalysts of two phase components, which may lose their performance due to gradually deteriorated interface conditions during their applications. In this work, a simple solvothermal process was developed to synthesize Bi2WO6 microspheres constructed by aggregated nanoflakes. The pure phase Bi2WO6 was found to possess the photocatalytic “memory” effect through the trapping and release of photogenerated electrons by the reversible chemical state change of W component in the (WO4)2− layers. When the illumination was switched off, Bi2WO6 microspheres continuously produced H2O2 in the dark as those trapped photogenerated electrons were gradually released to react with O2 through the two-electron O2 reduction process, resulting in the continuous disinfection of Escherichia coli bacteria in the dark through the photocatalytic “memory” effect. No deterioration of their cycling H2O2 production performance in the dark was observed, which verified their stable photocatalytic “memory” effect.

Electrochemically catalytic conversions have attracted worldwide interest as promising routes to reach a sustainable and green energy cycle. The exploration of efficient electrocatalysts is one of the key tasks, in which the majority has focused on devising new active centers; however, mass transport that determines the reactant supply and the conductance of electrolyte ions and electrons is often overlooked. Here, we report on spatially locating active centers into parallelly bimodal mesopores by precisely engineering mesopore geometries, through which the contribution of the paralleled transport channels to the activity of gas-consuming reactions was quantitatively determined. Under identical conditions, bimodal mesoporous carbon-based electrocatalysts displayed a 2.9 times higher CO partial current density than monomodal mesoporous catalysts for CO2-to-CO conversion in the kinetic region of −1.1 V vs. RHE. Likewise, the strong correlation between the activity enhancement and the bimodal mesopore geometry was verified for supported molecular catalysts and applicable to other gas-consuming reactions such as the O2 reduction reaction. These encouraging results offer a fresh and general idea to advance electrocatalysts by pore geometry engineering on the mesoscale.

A general interest in harnessing the oxidizing power of dioxygen (O2) continues to motivate research efforts on bioinspired and biomimetic complexes to better understand how metalloenzymes mediate these reactions. The ubiquity of Fe- and Cu-based enzymes attracts significant attention and has resulted in many noteworthy developments for abiotic systems interested in direct O2 reduction and small molecule activation. However, despite the existence of Mn-based metalloenzymes with important O2-dependent activity, there has been comparatively less focus on the development of these analogues relative to Fe- and Cu-systems. In this Perspective, we summarize important contributions to the development of bioinspired mononuclear Mn complexes for O2 activation and studies on their reactivity, emphasizing important design parameters in the primary and secondary coordination spheres and outlining mechanistic trends.

The selective two-electron O2 reduction reaction (2e− ORR) represents a green, mild, and on-site means of synthesizing H2O2. However, its practical feasibility depends on the development of advanced electrocatalysts, and limited experimental work has been done on non-precious-metal-based materials for the H2O2 electrogeneration in acids. Our study here introduces NiS2 nanosheets for the first time as an efficient electrocatalyst for the 2e− ORR under acidic conditions. In 0.05 M H2SO4, the NiS2 catalyst shows an onset overpotential of ∼130 mV and offers high selectivity (H2O2 percentage up to 99%). Moreover, the NiS2 catalyst attains the largest faradaic efficiency of 98% and the highest H2O2 yield rate of 109 ppm h−1 at 0.456 V and 0.156 V in the H-cell testing, respectively. The catalytic mechanism is revealed by theoretical calculations.

Hydrogen peroxide is an important high-energy product widely used in various fields. Highly efficient semiconductor photocatalysts, especially those that can produce H2O2 both from water oxidation and O2 reduction, are eagerly desired. In this work, BiOCl nanosheets with preferentially exposed (001) and (010) facets were synthesized via a simple hydrothermal method. The facet-dependent photocatalytic H2O2 generation activities of these BiOCl nanosheets were assessed. The hydrogen peroxide evolution rate of BiOCl(001) is about 2-fold higher than that of BiOCl(010), which is assigned to the higher separation efficiency of photogenerated charge carriers. Interestingly, both the EPR study and active species trapping experiments demonstrate that the generation of H2O2 on the BiOCl(001) photocatalyst mostly originates from sequential two step single-electron O2 reduction, while there are two pathways for photocatalytic H2O2 production on BiOCl(010), from both oxygen reduction and water oxidation. This work offers a new strategy to pursue highly efficient semiconductor photocatalysts with two pathways for H2O2 production from both water oxidation and O2 reduction.

Development of efficient and affordable catalytic systems for direct H2O2 production from abundant resources is necessary to replace the current anthraquinone process and also to enable broader use...

Screening catalysts with high performance for the O2 electroreduction reaction (ORR) is urgently needed for the renewable energy technology. A universal descriptor with easily accessible properties...

Homogeneous ORR catalyzed by cobalt macrocycles typically leads to selective 2e/2H+ reduction of O2 to H2O2; however, variations in the reaction conditions make it difficult to compare the performa...

Efficient photocatalytic reduction of electron acceptors is highly desirable for cathodic photoelectrochemical (PEC) sensors. Here, we report a facile and controllable strategy to tailor surface ox...

Photocatalytic production of green oxidation reagents as an economical and environmental-friendly process is a promising strategy to replace the traditional production processes. In the present study, a series of 1.0 wt% Pt/WO3 photocatalysts with different surface chemical states of Pt were successfully fabricated. The different surface metallic Pt (Pt0) and oxidized Pt (PtOx) ratios on WO3 showed significant effects on the photocatalytic activities for strong oxidants of peroxydisulfate ( $$ {\text{S}}_{ 2} {\text{O}}_{8}^{2 - } $$ ) and hydrogen peroxide (H2O2) formations. It is proposed that surface Pt0 and PtOx functioned as reduction site for O2 reduction to H2O and oxidation site for H2O oxidation to H2O2, respectively, during the photocatalytic process. As a result, a higher surface composition of Pt0 prepared using photodeposition (PD) method led to the formation of higher amount of $$ {\text{S}}_{ 2} {\text{O}}_{8}^{2 - } $$ . On the other hand, PtOx-loaded WO3 using impregnation (IM) method showed significant formations of $$ {\text{S}}_{ 2} {\text{O}}_{8}^{2 - } $$ and H2O2 simultaneously. This work provided a new idea for the design of noble metal Pt-supported WO3 for efficiently photocatalytic generation of $$ {\text{S}}_{ 2} {\text{O}}_{8}^{2 - } $$ and H2O2.

Electrochemical synthesis of hydrogen peroxide (H2O2) provides a clean and safe technology for large-scale H2O2 production. The core of this project is the development of highly active and highly selective catalysts. Recent studies demonstrate that carbonaceous materials are favorable catalysts because of their low-cost and tunable surface structures. This brief review first summarizes the strategies of carbonaceous material engineering for selective two-electron O2 reduction reaction and discusses potential mechanisms. In addition, several device designs using carbonaceous materials as catalysts for H2O2 production are introduced. Finally, research directions are proposed for practical application and performance improvement.

Microbiological Fe(III) reduction under oxic and acidic conditions in acid mine drainage (AMD)-impacted systems is surprising, given the greater energetic favorability of O2 reduction than Fe(III) ...

The reduction of dioxygen (O2) is of vital importance to energy-related reactions. In biology, respiration uses O2 reduction as a thermodynamic sink, whereas fuel cells pair the oxygen reduction re...

The mechanisms for O2 reduction and H2O/H2O2 formation on Co–corrin and Co–porphyrin cathode surfaces of the proton exchange membrane fuel cell (PEMFC) systems have been studied by hybrid Hartree–F...

Green reactions not only provide us chemical products without any pollution, but also offer us the viable technology to realize difficult tasks in normal conditions. Photo-, photoelectro-, and electrocatalytic reactions are indeed powerful tools to help us to embrace bright future. Especially, some gas-involved reactions are extremely useful to change our life environments from energy systems to liquid fuels and cost-effective products, such as H2 evolution (H2 production), O2 evolution/reduction, CO2 reduction, N2 reduction (or N2 fixation) reactions. We can provide fuel cells clean H2 for electric vehicles from H2 evolution reaction (HER), at the same time, we also need highly efficient O2 reduction reaction (ORR) in fuel cells for improving the reaction kinetics. Moreover, we can get the clean oxidant O2 from water through O2 evolution reaction (OER), and carry out some reactions without posing any pollution to reaction systems. Furthermore, we can translate the greenhouse gas CO2 into useful liquid fuels through CO2 reduction reaction (CRR). Last but not the least, we can get ammonia from N2 reduction reaction (NRR), which can decrease energy input compared to the traditional Hubble process. These reactions, such as HER, ORR, OER, CRR, and NRR could be realized through solar-, photoelectro- and electro-assisted ways. For them, the catalysts used play crucial roles in determining the efficiency and kinds of products, so we should consider the efficiency of catalysts. However, the cost, synthetic methods of catalysts should also be considered. Nowadays, significant progress has been achieved, however, many challenges still exist, reaction systems, catalysts underlying mechanisms, and so on. As extremely active fields, we should pay attention to them. Under the background, it has motivated us to contribute with a roadmap on ‘Gas-Involved Photo- and Electro-Catalysis’.

Development of nonprecious catalysts for O2 reduction reactions based on N4 macrocyclic transition-metal (TM) complexes demands a comprehensive understanding of the microscopic nature of O2 interac...

Oxygen reduction is a critical half reaction in renewable fuel cell development and a key step in the development of aerobic oxidation reactions. Herein, we report rapid two-electron O2 reduction by a d0 ZrIV center with an appended redox-active Co-I site serving as an electron reservoir. The early/late heterobimetallic Zr/Co complex (THF)Zr(MesNP iPr2)3CoCN tBu (1) reacts readily with O2 and O atom transfer reagents to generate reactive oxygenated species including terminal peroxo and oxo complexes, (O2)Zr(MesNP iPr2)3CoCN tBu (2) and O≡Zr(MesNP iPr2)3CoCN tBu (3). The bimetallic Zr/Co complex provides a new cooperative synthetic pathway to promote multielectron redox processes such as oxygen reduction, with each metal playing a distinct role as a substrate binding site or redox mediator.

Significance Most forms of life on Earth cannot exist without photosynthesis. Our food and atmosphere depend on it. To obtain high photosynthetic yields, light energy must be efficiently coupled to the fixation of CO2 into organic molecules. Suboptimal environmental conditions can severely impact the conversion of light energy to biomass and lead to reactive oxygen production, which in turn can cause cellular damage and loss of productivity. Hence, plants, algae, and photosynthetic bacteria have evolved a network of alternative outlets to sustain the flow of photosynthetically derived electrons. Our work is focused on the nature and integration of these outlets, which will inform a rational engineering of crop plants and algae to optimize photosynthesis and meet the increased global demand for food., Environmental stresses dramatically impact the balance between the production of photosynthetically derived energetic electrons and Calvin–Benson–Bassham cycle (CBBC) activity; an imbalance promotes accumulation of reactive oxygen species and causes cell damage. Hence, photosynthetic organisms have developed several strategies to route electrons toward alternative outlets that allow for storage or harmless dissipation of their energy. In this work, we explore the activities of three essential outlets associated with Chlamydomonas reinhardtii photosynthetic electron transport: (i) reduction of O2 to H2O through flavodiiron proteins (FLVs) and (ii) plastid terminal oxidases (PTOX) and (iii) the synthesis of starch. Real-time measurements of O2 exchange have demonstrated that FLVs immediately engage during dark-to-light transitions, allowing electron transport when the CBBC is not fully activated. Under these conditions, we quantified maximal FLV activity and its overall capacity to direct photosynthetic electrons toward O2 reduction. However, when starch synthesis is compromised, a greater proportion of the electrons is directed toward O2 reduction through both the FLVs and PTOX, suggesting an important role for starch synthesis in priming/regulating CBBC and electron transport. Moreover, partitioning energized electrons between sustainable (starch; energetic electrons are recaptured) and nonsustainable (H2O; energetic electrons are not recaptured) outlets is part of the energy management strategy of photosynthetic organisms that allows them to cope with the fluctuating conditions encountered in nature. Finally, unmasking the repertoire and control of such energetic reactions offers new directions for rational redesign and optimization of photosynthesis to satisfy global demands for food and other resources.

International audience; Net photosynthetic assimilation in C3 plants is mostly viewed as a simple balance between CO2 fixation by Rubisco‐catalyzed carboxylation and CO2 production by photorespiration (and to a lower extent, by day respiration) that can be easily manipulated during gas exchange experiments using the CO2:O2 ratio of the environment. However, it now becomes clear that it is not so simple, because the photosynthetic response to gaseous conditions involves ‘ancillary’ metabolisms, even in the short‐term. That is, carbon and nitrogen utilization by pathways other than the Calvin cycle and the photorespiratory cycle, as well as rapid signaling events, can influence the observed rate of net photosynthesis. The potential impact of such ancillary metabolisms is assessed as well as how it must be taken into account to avoid misinterpretation of photosynthetic CO2 response curves or low O2 effects in C3 leaves.

In this work, CuWO4 is prepared and its effect of improving photocatalytic degradation of atrazine by TiO2 as well as the synergetic mechanism is studied. Results show that the addition of CuWO4 (50 mg/L) into the reaction system can significantly enhance the efficiency of atrazine degradation, resulting in an increased degradation efficiency of 92.1% after 270 min, which is 1.94 times higher than that of the single TiO2. As the sintering temperate of CuWO4 was increased, the degradation efficiency of atrazine increased initially and then deceased after reaching a maximum at 500 °C. The origin of the synergistic effect of TiO2-CuWO4 is attributed to the introduction of solid CuWO4. The photochemical test results indicate that the photogenerated electrons transfer from irradiated TiO2 to CuWO4, which is beneficial to the O2 reduction and H2O2 formation in aqueous solution thus promoting the photocatalytic activity of TiO2. These observations unveil the importance of improving photocatalytic activity of TiO2 with Cu-bearing semiconductors.

Photocatalytic O2 reduction reactions proceeded to produce H2O2 using a diprotonated saddle-distorted dodecaphenylporphyrin as a photocatalyst. The quantum yield (12%), the turnover number (3000 for 6 h), and the turnover frequency (500 h−1) are achieved in photocatalytic systems based on free-base porphyrins for the first time. The photocatalytic reaction mechanism has been revealed by ns-laser flash photolysis and kinetic analysis.

We report the synthesis of cobalt nanoparticles supported on nitrogen-doped carbon (CoNPs@N/C), which can reduce O2 into H2O2 with high selectivity (up to 93%) in 0.1 M KOH electrolyte and retains >90% activity even after 10 h polarization. The catalyst achieves a current density of 1 mA cm–2 at 0.76 V(RHE) and a peroxide production rate of ∼3.8molH2O2 gCo–1 h–1 over a 10 h period. Our study also highlights the requirement for good peroxide production catalysts to be poor hydrogen peroxide disproportionation catalysts. We show how the high activity of the CoNPs@N/C catalyst is correlated with low activity toward the peroxide disproportionation reaction.

Porphyrins are archetypal ligands in inorganic chemistry. The last 10 years have seen important new advances in the use of metalloporphyrins as catalysts in the activation and reduction of small molecules, in particular O2 and CO2 . Recent developments of new molecular designs, scaling relationships, and theoretical modeling of mechanisms have rapidly advanced the utility of porphyrins as electrocatalysts. This Minireview focuses on the summary and evaluation of recent developments of metalloporphyrin O2 and CO2 reduction electrocatalysts, with an emphasis on contrasting homogeneous and heterogeneous electrocatalysis. Comparisons for proposed reaction mechanisms are provided for both CO2 and O2 reduction, and ideas are proposed about how lessons from the last decade of research can lead to the development of practical, applied porphyrin-derived catalysts.

Coupling of metal oxidation in crevice corrosion to both O2 reduction on surfaces external to the crevice and H+ reduction occurring within the crevice, was studied using a galvanostatic crevice corrosion technique in conjunction with weight loss analyses. Results suggest internal H+ reduction is a significant contributor to the crevice corrosion of the studied alloys in 5 M NaCl at 120 °C. Repeat experiments suggest damage can be as much as doubled by H+ reduction. This process, however, can be minimized by alloying additions of Mo, which permit the deposition of Mo-rich corrosion products within an active crevice. Due to difficulties experienced during corrosion product removal, the results presented herein are anticipated to be underestimates of the actual extent of this process. Consequently, damage predictions based on the availability of O2 and other oxidants in the service environment may significantly underestimate the actual extent of corrosion on Ni-Cr-Mo alloys.

Here we use in situ small and wide angle X-ray scattering to elucidate unexpected mechanistic insights of the O2 reduction mechanism in Li-O2 batteries.

In this study, on the basis of hierarchical CuInS2-based heterostructure, a novel cathodic photoelectrochemical (PEC) enzymatic bioanalysis of the sarcosine detection was reported. Specifically, heterostructured CuInS2/NiO/ITO photocathode was prepared and sarcosine oxidases (SOx) were integrated for the construction of the enzymatic biosensor. In the bioanalysis, the O2-dependent suppression of the cathodic photocurrent can be observed due to the competition between the as-fabricated O2-sensitive photocathode and the SOx-catalytic event toward O2 reduction. Based on the sarcosine-controlled O2 concentration, a novel photocathodic enzymatic biosensor could be realized for the sensitive and specific sarcosine detection. This work manifested the great potential of CuInS2-based heterostructure as a novel platform for future PEC bioanalytical development and also a PEC method for sarcosine detection, which could be easily extended to numerous other enzymatic systems and to our knowledge has not been reported. This work is expected to stimulate more interest in the design and implementation of numerous CuInS2-based heterostructured photocathodic enzymatic sensing.

First principles calculations were performed to cast insight into the mechanism of the improvement of O2 reduction reaction (ORR) activity by Zn and H interstitials on the anatase TiO2 (101) surface. For the Zn-modified anatase TiO2 (101) surface, both surface and subsurface Zn interstitials could contribute to O2 adsorption and dissociation, but the dissociation barriers of O2 molecules are still too high, which limits the ORR activity. After a H adatom is introduced onto the Zn-modified anatase TiO2 (101) surface, the highest energy barriers are greatly reduced compared with those of the Zn-modified surface. Meanwhile, it is observed that the dissociation barriers decrease almost linearly with the increase of the charge difference of adsorption O2 between initial and transition state configurations. Specifically, subsurface Zn and surface H interstitials facilitate O2 dissociation and subsequent oxidation reactions, and further frequency analysis shows that these dissociation processes are frequent even at the room temperature of 300 K. In a word, this work provides a theoretical support to design a high ORR activity catalyst of the TiO2 nanocrystal comparable to precious Pt catalysts.

Ni2P hollow microspheres were synthesized and examined as an electrocatalyst for both O2 evolution and reduction reactions. This hollow microsphere structure, assembled from ultrathin nanosheets, has a high surface-to-volume ratio and is beneficial for fast charge transfer and mass diffusion. This Ni2P material is efficient for water oxidation, achieving a 10 mA cm−2 current at a 280 mV overpotential. It is also effective in catalyzing the reduction of O2 with an onset potential of 0.92 V, representing a rare example of Ni phosphides as O2 reduction catalysts.

Translating homogeneous electrocatalysts to surface-immobilized electrocatalysts, while maintaining catalytic activity, has long been a research challenge. In this issue of Joule, Le Goff and coworkers report a surface-confined dinuclear copper electrocatalyst for O2 reduction that mimics the active site of multi-copper oxidases.

Recently in Joule, Preger et al. reported the development of a hydroquinone-based redox mediator in an acidic H2-O2 fuel cell. It facilitates O2 reduction in a catalyzed packed-bed reactor, enabling a maximum power density > 100 mW/cm2 and several hours of stable operation.

Summary Currently, bioelectrocatalytic devices such as biofuel cells and bioreactors are recognized as new environment-friendly devices for the production of electricity and valuable products. Thus far, systems have been improved from the viewpoints of enzymes and electrodes. A gas diffusion bioelectrode (GDBE) is one of the best approaches to improve electrode systems. This system has been remarkably developed and essentially employed in bioelectrocatalytic systems with gaseous substrates to realize high-speed H2 oxidation and O2 reduction for biofuel cells and to realize the high-speed bioelectrocatalytic reduction of CO2. GDBEs permit the enzymes to directly use gaseous substrates, and it is imperative that the electrodes exhibit suitable porosity, conductivity, and hydrophobicity/hydrophilicity balance for the gas permeation and enzyme reaction at the bio-three-phase interface of GDBEs. In this review article, the major factors of GDBEs are discussed by highlighting recent remarkable contributions and challenges.

In the past decade, the aprotic lithiumâoxygen (Liî¸O2) battery has generated a great deal of interest because theoretically it can store more energy than today's lithium-ion batteries. Although considerable research efforts have been devoted to the R&D of this potentially disruptive technology, many scientific and engineering obstacles still remain to be addressed before a practical device could be realized. In this review, we summarize recent advances in the fundamental understanding of the O2 electrochemistry in Liî¸O2 batteries, including the O2 reduction to Li2O2 on discharge and the reverse Li2O2 oxidation on recharge and factors that exert strong influences on the redox of O2/Li2O2. In addition, challenges and perspectives are also provided for the future study of Liî¸O2 batteries. Keywords: Lithiumâoxygen battery, Oxygen electrochemistry, Mechanism

The oxygen reduction mechanism and time evolution behavior were studied for porous La0.5-xPrxBa0.5CoO3-δ (LPBC) electrodes deposited onto Ce0.9Gd0.1O1.95 electrolytes. Electrochemical impedance spectroscopy (EIS) measurements, performed between 400 and 800 °C as a function of pO2, show that the electrochemical response is limited by O2-gas diffusion and surface reaction (O-surface exchange + O-ion diffusion). The time evolution of the cathode resistance at 700 °C in air shows an increase from 0.03 to 0.05 Ωcm2 after 280 h of testing. Three-dimensional (3D) tomographic using focused ion beam–scanning electron microscopy (FIB-SEM) showed little changes of microstructure after the ageing. The increase in resistance was explained by an increase in the amount of a water-soluble Ba-rich surface phase by a factor of 2, after ageing of the LPBC electrode, by an etching procedure coupled with inductively coupled plasma-optical emission spectrometry (ICP-OES). Fil: Garcés, Diana Andrea. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Wang, Hongqian. Northwestern University; Estados Unidos Fil: Barnett, Scott A.. Northwestern University; Estados Unidos Fil: Leyva, Ana Gabriela. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Universidad Nacional de San Martín; Argentina Fil: Mogni, Liliana Verónica. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

A facile approach to prepare Cu complexes for an efficient oxygen reduction reaction (ORR) was developed. Copper complexes of 5-nitrophenanthroline were sandwiched between polyvinylimidazole layers wrapped on carbon nanotubes, which showed ORR activity comparable to a Pt/C catalyst in alkaline media.

The sluggish kinetics and side reactions of the oxygen reduction reaction have impeded deployment of proton-exchange-membrane fuel cells. A recent article ( Xie et al .) introduces an efficient nonprecious metal catalyst (Fe2N6) that enhances the kinetics of 4-electron O2 reduction by more than seven times compared with that of the well-documented single-site FeN4 catalysts.

Cobalt porphyrins have been shown to electrocatalyze O2 reduction as well as H2 evolution. A cobalt porphyrin is synthesized when two electron-withdrawing groups are used in an attempt to reduce the overpotential involved in O2 reduction and H2 evolution. The results show that in the case of O2 reduction, instead of reduction of overpotential, the selectivity for O2 reduction changes to 2e-/2H+ to produce H2O2. In the case of H2 evolution, the CoI state is incapable of catalyzing H+ reduction. Rather, a CoIII-H species needs to be reduced to CoII-H before H2 can be produced. There results add to the ongoing investigations into the factors that control the rates, overpotential and selectivity of these important cathodic processes.

Tungsten oxide (WO3) is regarded as a promising visible-light-sensitive photocatalyst, but its activity is not high. Further enhancement of its activity has been anticipated using techniques such as loading of a cocatalyst to apply the oxide to indoor environmental remediation; Pt has been reported as a good cocatalyst for WO3 photocatalysis. However, Pt is precious and expensive metal. Thus, in this study, we sought to find a ubiquitous cocatalyst and suitable photocatalyst system. As a result, this study revealed that loading a ubiquitous material of red-clay enhanced WO3 photocatalytic activity remarkably. As photocatalyst samples, mixtures consisting of the clay and WO3 with different weight ratios were prepared using a simple kneading method. Their photocatalytic activity was evaluated from decomposition of harmful organic contaminant, 2-propanol into CO2 under visible-light irradiation. The WO3 with 10% of the clay loading showed the highest activity among the samples and much higher activity than pure WO3. This higher activity might derive from the clay’s promotion of H2O2 decomposition and charge separation (holes and electrons). The H2O2 was generated from photocatalytic O2 reduction. This formation and accumulation on the pure WO3 surface led to decreased activity.

Photocatalytic H2O2 production by O2 reduction is an environmental-friendly process for solar light conversion to chemical energy. In this work, Ti3C2 MXene was used as a non-noble metal cocatalyst to load on P25 as Ti3C2/TiO2 (TC/TO) photocatalysts for photocatalytic H2O2 synthesis. A H2O2 formation rate (179.7 μmol L−1 h−1) of the optimized 10 %-TC/TO composite was obtained to be over 21 folds as high as that of P25 under UV light. Radical quenching experiments and superoxide radical detection confirmed the superoxide radical as the primary intermediate, suggesting the O2 reduction in two-step single-electron indirect reaction. The higher activity of TC/TO can be attributed to the functions of Ti3C2 MXene in accelerating the separation and transfer of photogenerated electron-hole pairs, suppressing their recombination, and blocking the surface Ti OOH formation. This work proves the promising roles of Ti3C2 MXene in the photocatalytic reaction and further expands their new applications in photocatalysis.

With the drastic increase of global energy and sensing demand in this century, the development of sustainable energy and highly sensitive sensor has become progressively paramount. Electrochemical energy storage devices with the ability to store sustainable energy, electrochemical-sensing and electrocatalysis technologies such as O2 reduction reaction (ORR), O2 evolution reaction (OER), H2 evolution reaction (HER), CO2 reduction reaction (CRR), and N2 reduction reaction (NRR) are highly desired. The performances of these devices tightly rely on the electrode materials, which has aroused extensive attention on the exploitations of novel electrode active substances. Due to the outstanding structural designability, large specific surface area and adjustable active sites, electrically conductive metal-organic frameworks with redox-activity (ECMOFs) are regarded as the capable candidates of active substances for those electrochemical applications. This review introduces the conductive mechanisms of ECMOFs, provides the design strategies of ECMOFs electrodes and summarizes the recent advances on ECMOFs in electrochemical sensing, electrochemical energy storage and electrocatalysts in detail. Finally, the challenges and outlook of ECMOFs in the practical applications are systematically emphasized, which will open an avenue to the development of ECMOFs-based electrochemical devices.

This work discusses the effect of the crystal structure and microstructure on the electrocatalytic activity of Lanthanum-Barium cobaltite (LBC), evaluatedas IT-SOFC cathode. Two systems with similar microstructures (particle sizes dp 1?5 mm) are used to compare the effect of the crystal structure: the cubic La0.5Ba0.5CoO3-d with La/Ba cations randomly distributed, and a tetragonal LaBaCo2O6-d with La/Ba layered distribution. In addition, the effect of microstructure is studied by using a newsol-gel route which allows obtaining LaBaCo2O6-d with smallest particle size (dp 500 nm). The electrode reactionisstudied by electrochemical impedance spectroscopy (EIS) as a function of temperature (T) and oxygen partial pressure (pO2). The electrode polarization resistance (RC,P) presents two contributions, a low frequency (RLF) and a high frequency Gerischer-resistance (RG). On one side, RLF, associated to the O2-gas diffusion across the gas layer boundary, presents low activation energy (Ea) and is proportional to pO2 -1,presenting the same values regardless the microstructure.On the other side, RG is in agreement with an O2-reduction mechanism co-limited by O-surface exchange and O-bulk diffusion. RG is strongly influenced by structure (trough the diffusion coefficient DV) and microstructure (inversely proportional to dp). Besides, RG decreases by reducing dp and by modifying the La/Ba ordering from layered to randomly distributed. Fil: Garcés, Diana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Soldati, Analía Leticia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Montenegro Hernandez, Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Caneiro, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Mogni, Liliana Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

Bilirubin oxidase (BOD) catalyzes 4e−-reduction of O2 into H2O and is one of the enzymes allowing direct electron transfer (DET)-type bioelectrocatalysis. Mesoporous carbon materials are often used for constructing BOD-modified DET-type biocathodes. We have examined the performance of several multi-walled carbon nanotubes (MWCNTs) as cathode platforms for BOD-catalyzed bioelectrocatalytic O2 reduction. It has been found that the length of MWCNTs is a very important factor to control the performance. The π-π conjugated system with the carboxy groups on the surface of MWCNTs plays an important role in enhancing the DET-type bioelectrocatalytic activity of BOD. Water-soluble MWCNT with the length of as short as 1 − 4 μm is the most suitable material among the MWCNTs examined, and they have been used to construct a mesoporous carbon electrode without any binder. The catalytic current density has reached a diffusion-controlled level for the first time for BOD at an electrode rotating rate of 4000 rpm and at 25 °C (8 mA cm−2).

Here, we demonstrate the use of phospholipid micelles to enhance O2 concentrations by two-fold at the surface of a bilirubin oxidase biocathode. Specifically, 1,2-diarachidoyl-sn-glycero-3-phosphocholine was used in a glucose enzymatic fuel cell to limit power losses due to O2 transport, even in a quiescent solution.