Capillary Effect-Enabled Water Electrolysis for Enhanced Electrochemical Ozone Production by Using Bulk Porous Electrode

Origin of the Activity of Electrochemical Ozone Production Over Rutile PbO2 Surfaces

Ozonation water treatment technology has attracted increasing attention due to its environmental benign and high efficiency. Rutile PbO2 is a promising anode material for electrochemical ozone production (EOP). However, the reaction mechanism underlying ozone production catalyzed by PbO2 was rarely studied and not well-understood, which was in part due to the overlook of the electrochemistry-driven formation of oxygen vacancy (OV) of PbO2. Herein, we unrevealed the origin of the EOP activity of PbO2 starting from the electrochemical surface state analysis using density functional theory (DFT) calculations, activity analysis, and catalytic volcano modeling. Interestingly, we found that under experimental EOP potential (i. e., a potential around 2.2 V vs. reversible hydrogen electrode), OV can still be generated easily on PbO2 surfaces. Our subsequent kinetic and thermodynamic analyses show that these OV sites on PbO2 surfaces are highly active for the EOP reaction through an interesting atomic oxygen (O*)-O2 coupled mechanism. In particular, rutile PbO2(101) with the "in-situ" generated OV exhibited superior EOP activities, outperforming the (111) and (110) surfaces. Finally, by catalytic volcano modeling, we found that PbO2 is close to the theoretical optimum of the reaction, suggesting a superior EOP performance of rutile PbO2. All these analyses are in good agreement with previous experimental observations in terms of EOP overpotentials. This study provides the first volcano model to explain why rutile PbO2 is among the best metal oxide materials for EOP and provides new design guidelines for this rarely studied but industrially promising reaction.

Engineering in situ growth of Au nanoclusters on hydrophilic paper fibres for fluorescence calligraphy-based chemical logic gates and information encryption

Gold nanoclusters (AuNCs) are a type of rising-star fluorescence nanomaterials, but their properties and applications are hindered by the multi-step synthesis and purification routes, as well as the lack of desired supporting substrates. To enhance optical performance and working efficiency, the synthesis and applications of AuNCs are suggested to be merged with emerging substrates. Herein, glutathione-modified hydrophilic rice papers are incubated in chloroauric acid aqueous solutions, and the oxidation-reduction reaction between glutathione and Au ions enables the in situ formation of fluorescent AuNCs on the solid fibres of rice papers. The in situ growth of fluorescent AuNCs on rice papers resulted in eye-catching fluorescence tracks, similar to traditional Chinese conventional calligraphy; thus, this fluoresence calligraphy is defined in this work. The entire process, including synthesis and signal responses, is extremely simple, rapid, and repeatable. Moreover, the diversity of additive chemical reagents in the studied rice papers resulted in responsive fluorescence calligraphy, and the as-synthesized AuNC materials exhibited high reliability and optical stability. Significantly, with the integration of synchronous formation and application of Au nanoclusters on hydrophilic paper substrates, high-performance logical gates and information encryption systems were constructed, remarkably facilitating the progress of molecular sensing and important information transmission.

Unraveling the Fluoride-Induced Interface Reconstruction Across Lead-Based Hierarchical MnO2 Anode in Zinc Electrowinning

Although the hierarchical manganese dioxide film electrode shows promise as a durable and catalytically active anode for zinc electrowinning, it often fails and deactivates when it is exposed to fluoride-rich environments. The lack of understanding regarding the mechanism behind fluoride-induced irreversible interface reconstruction hinders their practical application in large-scale energy-saving and pollution-reduction efforts. Here, we conducted multidimensional operando investigations to gain insights into the dynamic evolution across the film electrode interface with temporal and spatial resolution. Our findings reveal that electroosmosis of F- initially triggers structural collapse and subsequent reconstruction of [MnO6] units, followed by interaction with the spontaneous oxide film at the surface of lead substrate. Experimental studies and theoretical calculations indicate that F- facilitates the irreversible transformation of γ-MnO2 into more stable yet protective catalytic dual-defective α-MnO2. Additionally, lower levels of F- at the interface promote a change in microenvironmental pH within porous PbSO4, triggering the development of microporous corrosion-resistant β-PbO2 as the dominant phase. The combined effects of MnO2 and interphase evolution effectively explain the abnormally elevated oxygen evolution overpotential. Then, the proposed appropriate application scenarios based on the corrosion behavior will serve as a practical guide for the implementation of the hierarchical manganese dioxide film electrode.

Interplay between Catalyst Corrosion and Homogeneous Reactive Oxygen Species in Electrochemical Ozone Production

Electrochemical ozone production (EOP), a six-electron water oxidation reaction, offers promising avenues for creating value-added oxidants and disinfectants. However, progress in this field is slowed by a dearth of understanding of fundamental reaction mechanisms. In this work, we combine experimental electrochemistry, spectroscopic detection of reactive oxygen species (ROS), oxygen-anion chemical ionization mass spectrometry, and computational quantum chemistry calculations to determine a plausible reaction mechanism on nickel- and antimony-doped tin oxide (Ni/Sb-SnO2, NATO), one of the most selective EOP catalysts. Antimony doping is shown to increase the conductivity of the catalyst, leading to improved electrochemical performance. Spectroscopic analysis and electrochemical experiments combined with quantum chemistry predictions reveal that hydrogen peroxide (H2O2) is a critical reaction intermediate. We propose that leached Ni4+ cations catalyze hydrogen peroxide into solution phase hydroperoxyl radicals (•OOH); these radicals are subsequently oxidized to ozone. Isotopic product analysis shows that ozone is generated catalytically from water and corrosively from the catalyst oxide lattice without regeneration of lattice oxygens. Further quantum chemistry calculations and thermodynamic analysis suggest that the electrochemical corrosion of tin oxide itself might generate hydrogen peroxide, which is then catalyzed to ozone. The proposed pathways explain both the roles of dopants in NATO and its lack of stability. Our study interrogates the possibility that instability and electrochemical activity are intrinsically linked through the formation of ROS. In doing so, we provide the first mechanism for EOP that is consistent with computational and experimental results and highlight the central challenge of instability as a target for future research efforts.

Mesoporous hydrogel electrodes with flexible frameworks exhibiting enhanced mass transport for the oxygen evolution reaction

Mesoporous hydrogel electrodes with unique flexible mesopores surrounded by CoOOH nanosheets were prepared via the electrochemical deposition of hybrid cobalt hydroxide nanosheets, exhibiting high oxygen evolution reaction activity at a high current density owing to the enhanced mass transport of oxygen molecules.

Nanoscale Metal Particle Modified Single-Atom Catalyst: Synthesis, Characterization, and Application

Single-atom catalysts (SACs) have attracted considerable attention in heterogeneous catalysis because of their well-defined active sites, maximum atomic utilization efficiency, and unique unsaturated coordinated structures. However, their effectiveness is limited to reactions requiring active sites containing multiple metal atoms. Furthermore, the loading amounts of single-atom sites must be restricted to prevent aggregation, which can adversely affect the catalytic performance despite the high activity of the individual atoms. The introduction of nanoscale metal particles (NMPs) into SACs (NMP-SACs) has proven to be an efficient approach for improving their catalytic performance. A comprehensive review is urgently needed to systematically introduce the synthesis, characterization, and application of NMP-SACs and the mechanisms behind their superior catalytic performance. This review first presents and classifies the different mechanisms through which NMPs enhance the performance of SACs. It then summarizes the currently reported synthetic strategies and state-of-the-art characterization techniques of NMP-SACs. Moreover, their application in electro/thermo/photocatalysis, and the reasons for their superior performance are discussed. Finally, the challenges and perspectives of NMP-SACs for the future design of advanced catalysts are addressed.

Packed OV-SnO2-Sb bead-electrodes for enhanced electrocatalytic oxidation of micropollutants in water

Electrocatalytic oxidation is an appealing treatment option for emerging micropollutants in wastewater, however, the limited reactive surface area and short service lifetime of planar electrodes hinder their industrial applications. This study introduces an innovative electrochemical wastewater treatment technology that employs packed bead-electrodes (PBE) as a dynamic electrocatalytic filter on a dimensionally stable anode (DSA) acting as a current collector. By using PBE, the electroactive volume is expanded beyond the vicinity of the common planar anode to the thick porous media of PBE with a vast electrocatalytic surface area. This greatly enhances the efficiency of electrochemical degradation of micropollutants. The OV-SnO2-Sb PBE filter achieved a nearly 100 % degradation of moxifloxacin (MOX) in under 2 min of single-pass filtration, with a degradation rate over an order of magnitude higher than the conventional electrochemical oxidation processes. The generation of abundant radical species (•OH) and non-radical species (1O2 and O3), along with the enhanced direct oxidation, led to the outstanding performance of the charged PBE system in MOX degradation. The OV-SnO2-Sb PBE was remarkably stable, and the separation between the electroactive PBE layer and the base Ti anode allows for easy renewal of the bead-electrode materials and scaling up of the system for practical applications. Overall, our study presents a dynamic electroactive PBE that advances the electrocatalytic oxidation technology for effective control of emerging pollutants in the water environment. This technology has the potential to revolutionize electrochemical wastewater treatment and contribute to a more sustainable future environment.

PbO2 materials for electrochemical environmental engineering: A review on synthesis and applications

Lead dioxide (PbO₂) materials have been widely employed in various fields such as batteries, electrochemical engineering, and more recently environmental engineering as anode materials, due to their unique physicochemical properties. Key performances of PbO₂ electrodes, such as energy efficiency and space-time yield, are influenced by morphological as well as compositional factors. Micro-nano structure regulation and decoration of metal/non-metal on PbO₂ is an outstanding technique to revamp its electrocatalytic activities and enhance environmental engineering efficiency. The aim of this review is to comprehensively summarize the recent research progress in the morphology control, the structure constructions, and the element doping of PbO₂ materials, further with many environmental application cases evaluated. Concerning electrochemical environmental engineering, the lead dioxide employed in chemical oxygen demand detection, ozone generators, and wastewater treatment has been comprehensively reviewed. In addition, the future research perspectives, challenges and the opportunities on PbO₂ materials for environmental applications are proposed.

Oxygen Vacancy Defects and a Field Effect-Mediated ZnO/WO2.92 Heterojunction for Enhanced Corrosion Resistance

The heterojunction constructed by tungsten oxide and zinc oxide materials can improve the problem of easy deactivation of electrons, which is a new and effective strategy for realizing anticorrosion. Here, the ZnO/WO_2.92 heterojunction modified by oxygen vacancies (OVs) serving as the photoelectric conversion center was not consumed to provide continuous light-induced protection for steel, and the impedance value was increased by 185.35% compared to that of epoxy resin after 72 h of corrosion. The enhanced anticorrosion activity was due to OV modification leading to oxygen adsorption and electron capture, which inhibited the cathodic corrosion reaction and effectively hindered electron transport. Additionally, the localized surface plasmon resonance effect produced by OVs improved light utilization efficiency and increased electron density, which enabled numerous photoelectrons to gather on the surface of the iron substrate to reduce the corrosion rate of metals. Besides, the cascade effect of the ZnO/WO_2.92 heterojunction promoted the transfer of e^-/h⁺ to form an electric field that allowed the directional flow of electrons to inhibit the anode dissolution process. Thus, exploring the corrosion reaction involving OVs and heterojunction structures was of great significance to the development of nonsacrificial and efficient anticorrosion materials.

Steering CO2 electroreduction toward ethanol production by a surface-bound Ru polypyridyl carbene catalyst on N-doped porous carbon

Electrochemical reduction of CO₂ to multicarbon products is a significant challenge, especially for molecular complexes. We report here CO₂ reduction to multicarbon products based on a Ru(II) polypyridyl carbene complex that is immobilized on an N-doped porous carbon (RuPC/NPC) electrode. The catalyst utilizes the synergistic effects of the Ru(II) polypyridyl carbene complex and the NPC interface to steer CO₂ reduction toward C2 production at low overpotentials. In 0.5 M KHCO₃/CO₂ aqueous solutions, Faradaic efficiencies of 31.0 to 38.4% have been obtained for C2 production at -0.87 to -1.07 V (vs. normal hydrogen electrode) with 21.0 to 27.5% for ethanol and 7.1 to 12.5% for acetate. Syngas is also produced with adjustable H₂/CO mole ratios of 2.0 to 2.9. The RuPC/NPC electrocatalyst maintains its activity during 3-h CO₂-reduction periods.

Bioinspired Fe3C@C as Highly Efficient Electrocatalyst for Nitrogen Reduction Reaction under Ambient Conditions

Developing highly efficient non-precious-metal catalysts for electrochemical reduction reaction is vital for artificial nitrogen fixation under ambient conditions. Herein, we report a bioinspired Fe₃C@C composite as an efficient electrocatalyst for nitrogen reduction. The composite based on a leaf skeleton successfully replicates the natural vein structure with multichannels. The Fe₃C@C core-shell structure as the real active center contributes to selective electrocatalytic synthesis of ammonia from nitrogen with Faraday efficiency of 9.15% and production rate of 8.53 μg/(h mg_cat) or 12.80 μg/(h cm²) at a low potential of -0.2 V versus reversible hydrogen electrode (vs RHE), which is better than that of recently reported carbon- and iron-based materials, even comparable with that of noble-metal-based catalyst. Experiments with density functional theory calculations reveal that graphene-encapsulated Fe₃C nanoparticles can improve charge transfer due to core-shell interaction, beneficial for inducing active sites for N₂ adsorption and activation and thereby facilitate ammonia synthesis.

Influence of Mn2+ ions on the corrosion mechanism of lead-based anodes and the generation of heavy metal anode slime in zinc sulfate electrolyte

The influence of Mn²⁺ ions on the generation of heavy metal anode slime during zinc electrolysis industry was extensively investigated using several electrochemical methods, electron microscope technologies, and particle size analysis. Results showed that the Mn²⁺ could obviously promote oxygen evolution reaction (OER) and thereby weaken oxidation efficiency of Mn²⁺ (η_MnO2) and dissolution of Pb²⁺. The significant improvement in kinetic parameters for OER was found in electrolytes of 1 and 3 g/L Mn²⁺, but became unstable as the Mn²⁺ concentration increased to 10 g/L. This result was correlated with much different properties of oxide layers that its changes of microstructure are involved in, since it confirmed that the positive role of compact oxide layers in contributing to high corrosion resistance and activity for OER, but excessive Mn²⁺, resulted in its micromorphology of overthickness and instability. Such differences resulted from the effect of the Mn²⁺ concentration fluctuation on kinetic rates of the nucleation growth process. The formation and adsorption of intermediate MnO₂-OH_ads identified as the controlled step for Mn²⁺ catalyzing OER was also recommended. The generation mechanism of anode slime was found to be changed in essence due to varying Mn²⁺ concentrations. In electrolyte of 1 g/L Mn²⁺, results revealed that the root cause of excessive small suspended anode slime (around 20 μm) was the change of the initial pathway of Mn²⁺ electro-oxidation, whereas, it showed great improvement in the settling performance as the Mn²⁺ concentration was increased to 10 g/L. Considering the potential of optimizing Mn²⁺ concentrations as a cleaner approach to control anode slime, deepening the understanding of the impact mechanism of Mn²⁺ can provide new insights into intervention in the generation of anode slime.