Electronegative Phosphorus-Integrated Co2+ Active Sites for Enhanced Electrocatalytic Nitrogen Reduction.

In the quest for proficient electrocatalysts for ammonia's electrocatalytic nitrogen reduction, cobalt oxides, endowed with a rich d-electron reservoir, have emerged as frontrunners. Despite the previously evidenced prowess of CoO in this realm, its ammonia yield witnesses a pronounced decline as the reaction unfolds, a phenomenon linked to the electron attrition from its Co2+ active sites during electrocatalytic nitrogen reduction reaction (ENRR). To counteract this vulnerability, we harnessed electron-laden phosphorus (P) elements as dopants, aiming to recalibrate the electronic equilibrium of the pivotal Co active site, thereby bolstering both its catalytic performance and stability. Our empirical endeavors showcased the doped P-CoO's superior credentials: it delivered an impressive ammonia yield of 49.6 and, notably, a Faradaic efficiency (FE) of 9.6% at -0.2 V versus RHE, markedly eclipsing its undoped counterpart. Probing deeper, a suite of ex-situ techniques, complemented by rigorous theoretical evaluations, was deployed. This dual-pronged analysis unequivocally revealed CoO's propensity for an electron-driven valence metamorphosis to Co3+ post-ENRR. In stark contrast, P-CoO, fortified by P doping, exhibits a discernibly augmented ammonia yield. Crucially, P's intrinsic ability to staunch electron leakage from the active locus during ENRR ensures the preservation of the valence state, culminating in enhanced catalytic dynamism and fortitude. This investigation not only illuminates the intricacies of active site electronic modulation in ENRR but also charts a navigational beacon for further enhancements in this domain.

Unlocking Spin Gates of Transition Metal Oxides via Strain Stimuli to Augment Potassium Ion Storage.

Transition metal oxides (TMOs) are key in electrochemical energy storage, offering cost-effectiveness and a broad potential window. However, their full potential is limited by poor understanding of their slow reaction kinetics and stability issues. This study diverges from conventional complex nano-structuring, concentrating instead on spin-related charge transfer and orbital interactions to enhance the reaction dynamics and stability of TMOs during energy storage processes. We successfully reconfigured the orbital degeneracy and spin-dependent electronic occupancy by disrupting the symmetry of magnetic cobalt (Co) sites through straightforward strain stimuli. The key to this approach lies in the unfilled Co 3d shell, which serves as a spin-dependent regulator for carrier transfer and orbital interactions within the reaction. We observed that the opening of these 'spin gates' occurs during a transition from a symmetric low-spin state to an asymmetric high-spin state, resulting in enhanced reaction kinetics and maintained structural stability. Specifically, the spin-rearranged Al-Co3O4 exhibited a specific capacitance of 1371 F g-1, which is 38 % higher than that of unaltered Co3O4. These results not only shed light on the spin effects in magnetic TMOs but also establish a new paradigm for designing electrochemical energy storage materials with improved efficiency.

Modulating the d-Band Center of Palladium via Ethylene Glycol Modification: Accelerating Had Desorption for Enhanced Formate Electrooxidation.

This study addresses the critical challenge in alkaline direct formate fuel cells (DFFCs) of slow formate oxidation reaction (FOR) kinetics as a result of strong hydrogen intermediate (Had) adsorption on Pd catalysts. We developed WO3-supported Pd nanoparticles (EG-Pd/WO3) via an organic reduction method using ethylene glycol (EG), aiming to modulate the d-band center of Pd and alter Had adsorption dynamics. Cyclic voltammetry demonstrated significantly improved Had desorption kinetics in EG-Pd/WO3 catalysts. Density functional theory (DFT) calculations revealed that the presence of EG reduces the d-band center of Pd, leading to weaker Pd-H bonds and enhanced Had desorption during the FOR. This research provides a new approach to optimize catalyst efficiency in DFFCs, highlighting the potential for more effective and sustainable energy solutions through advanced material engineering.

Activation of MnO6 Units via an Interfacial Electric Field: Electron Injection into Mn t2g for Rapid and Stable Sodium Ion Storage in CeO2 /MnOx.

Manganese-based oxides (MnOx ) suffer from sluggish charge diffusion kinetics and poor cycling stability in sodium ion storage. Herein, an interfacial electric field (IEF) in CeO2 /MnOx is constructed to obtain high electronic/ionic conductivity and structural stability of MnOx . The as-designed CeO2 /MnOx exhibits a remarkable capacity of 397 F g-1 and favorable cyclic stability with 92.13% capacity retention after 10,000 cycles. Soft X-ray absorption spectroscopy and partial density of states results reveal that the electrons are substantially injected into the Mn t2g orbitals driven by the formed IEF. Correspondingly, the MnO6 units in MnOx are effectively activated, endowing the CeO2 /MnOx with fast charge transfer kinetics and high sodium ion storage capacity. Moreover, In situRaman verifies a remarkably increased structural stability of CeO2 /MnOx , which is attributed to the enhanced Mn─O bond strength and efficiently stabilized MnO6 units. Mechanism studies show that the downshift of Mn 3d-band center dramatically increases the Mn 3d-O 2p orbitals overlap, thus inhibiting the Jahn-Teller (J-T) distortion of MnOx during sodium ion insertion/extraction. This work develops an advanced strategy to achieve both fast and sustainable sodium ion storage in metal oxides-based energy materials.

Cu-Modified Palladium Catalysts: Boosting Formate Electrooxidation via Interfacially OHad-Driven Had Removal.

Direct formate fuel cells have gained traction due to their eco-friendly credentials and inherent safety. However, their potential is hampered by the kinetic challenges of the formate oxidation reaction (FOR) on Pd-based catalysts, chiefly due to the unfavorable adsorption of hydrogen species (Had). These species clog the active sites, hindering efficient catalysis. Here, we introduce a straightforward strategy to remedy this bottleneck by incorporating Pd with Cu to expedite the removal of Pd-Had in alkaline media. Notably, Cu plays a pivotal role in bolstering the concentration of hydroxyl adsorbates (OHad) on the surface of catalyst. These OHad species can react with Had, effectively unblocking the active sites for FOR. The as-synthesized catalyst of PdCu/C exhibits a superior FOR performance, boasting a remarkable mass activity of 3.62 A mg-1. Through CO-stripping voltammetry, we discern that the presence of Cu in Pd markedly speeds up the formation of adsorbed hydroxyl species (OHad) at diminished potentials. This, in turn, aids the oxidative removal of Pd-Had, leveraging a synergistic mechanism during FOR. Density functional theory computations further reveal intensified interactions between adsorbed oxygen species and intermediates, underscoring that the Cu-Pd interface exhibits greater oxyphilicity compared to pristine Pd. In this study, we present both experimental and theoretical corroborations, unequivocally highlighting that the integrated copper species markedly amplify the generation of OHad, ensuring efficient removal of Had. This work paves the way, shedding light on the strategic design of high-performing FOR catalysts.

Energizing Co Active Sites via d-Band Center Engineering in CeO2 -Co3 O4 Heterostructures: Interfacial Charge Transfer Enabling Efficient Nitrate Electrosynthesis.

The electrochemical nitrogen oxidation reaction (NOR) holds significant potential to revolutionize the traditional nitrate synthesis processes. However, the progression in NOR has been notably stymied due to the sluggish kinetics of initial N2 adsorption and activation processes. Herein, the research embarks on the development of a CeO2 -Co3 O4 heterostructure, strategically engineered to facilitate the electron transfer from CeO2 to Co3 O4 . This orchestrated transfer operates to amplify the d-band center of the Co active sites, thereby enhancing N2 adsorption and activation dynamics by strengthening the Co─N bond and diminishing the resilience of the N≡N bond. The synthesized CeO2 -Co3 O4 manifests promising prospects, showcasing a significant HNO3 yield of 37.96 µg h-1 mgcat -1 and an elevated Faradaic efficiency (FE) of 29.30% in a 0.1 m Na2 SO4 solution at 1.81 V versus RHE. Further substantiating these findings, an array of in situ methodologies coupled with DFT calculations vividly illustrate the augmented adsorption and activation of N2 on the surface of CeO2 -Co3 O4 heterostructure, resulting in a substantial reduction in the energy barrier pertinent to the rate-determining step within the NOR pathway. This research carves a promising pathway to amplify N2 adsorption throughout the electrochemical NOR operations and delineates a blueprint for crafting highly efficient NOR electrocatalysts.

High Flux and Stability of Cationic Intercalation in Transition-Metal Oxides: Unleashing the Potential of Mn t2g Orbital via Enhanced π-Donation.

Transition-metal oxides (TMOs) often struggle with challenges related to low electronic conductivity and unsatisfactory cyclic stability toward cationic intercalation. In this work, we tackle these issues by exploring an innovative strategy: leveraging heightened π-donation to activate the t2g orbital, thereby enhancing both electron/ion conductivity and structural stability of TMOs. We engineered Ni-doped layered manganese dioxide (Ni-MnO2), which is characterized by a distinctive Ni-O-Mn bridging configuration. Remarkably, Ni-MnO2 presents an impressive capacitance of 317 F g-1 and exhibits a robust cyclic stability, maintaining 81.58% of its original capacity even after 20,000 cycles. Mechanism investigations reveal that the incorporation of Ni-O-Mn configurations stimulates a heightened π-donation effect, which is beneficial to the π-type orbital hybridization involving the O 2p and the t2g orbital of Mn, thereby accelerating charge-transfer kinetics and activating the redox capacity of the t2g orbital. Additionally, the charge redistribution from Ni to the t2g orbital of Mn effectively elevates the low-energy orbital level of Mn, thus mitigating the undesirable Jahn-Teller distortion. This results in a subsequent decrease in the electron occupancy of the π*-antibonding orbital, which promotes an overall enhancement in structural stability. Our findings pave the way for an innovative paradigm in the development of fast and stable electrode materials for intercalation energy storage by activating the low orbitals of the TM center from a molecular orbital perspective.

Built-in Electric Field-Induced Work Function Reduction in C-Co3O4 for Efficient Electrochemical Nitrogen Reduction.

Co3O4 is a highly selective catalyst for the electrochemical conversion of N2 to NH3. However, the large work function (WF) of Co3O4 leads to unsatisfactory activity. To address this issue, a strong built-in electric field (BIEF) was constructed in Co3O4 by doping C atoms (C-Co3O4) to reduce the WF for improving the electrocatalytic performance. C-Co3O4 exhibited a remarkable NH3 yield of 38.5 µg h-1 mgcat-1 and a promoted FE of 15.1% at -0.3 V vs RHE, which were 2.2 and 1.9 times higher than those of pure Co3O4, respectively. Kelvin probe force microscopy (KPFM), zeta potential, and ultraviolet photoelectron spectrometry (UPS) confirmed the formation of strong BIEF and WF reduction in C-Co3O4. Additionally, in situ Raman measurements and density functional theory (DFT) calculations revealed the relationship between BIEF and WF and provided insights into the reaction mechanism. Our work offers valuable guidance for the design and development of more efficient nitrogen reduction catalysts.

Electrochemical Removal of Metal-Organic Complexes in Metal Plating Wastewater: A Comparative Study of Cu-EDTA and Ni-EDTA Removal Mechanisms.

Cu and Ni complexes with ethylenediaminetetraacetic acid (Cu/Ni-EDTA), which are commonly present in metal plating industry wastewaters, pose a serious threat to both the environment and human health due to their high toxicity and low biodegradability. In this study, the treatment of solutions containing either or both Cu-EDTA and Ni-EDTA using an electrochemical process is investigated under both oxidizing and reducing electrolysis conditions. Our results indicate that Cu-EDTA is decomplexed as a result of the cathodic reduction of Cu(II) with subsequent electrodeposition of Cu(0) at the cathode when the cathode potential is more negative than the reduction potential of Cu-EDTA to Cu(0). In contrast, the very negative reduction potential of Ni-EDTA to Ni(0) renders the direct reduction of EDTA-complexed Ni(II) at the cathode unimportant. The removal of Ni during the electrolysis process mainly occurs via anodic oxidation of EDTA in Ni-EDTA, with the resulting formation of low-molecular-weight organic acids and the release of Ni2+, which is subsequently deposited as Ni0 on the cathode. A kinetic model incorporating the key reactions occurring in the electrolysis process has been developed, which satisfactorily describes EDTA, Cu, Ni, and TOC removal. Overall, this study improves our understanding of the mechanism of removal of heavy metals from solution during the electrochemical advanced oxidation of metal plating wastewaters.

Boosting CO2 Electroreduction to C2H4 via Unconventional Hybridization: High-Order Ce4+ 4f and O 2p Interaction in Ce-Cu2O for Stabilizing Cu.

Efficient conversion of carbon dioxide (CO2) into value-added materials and feedstocks, powered by renewable electricity, presents a promising strategy to reduce greenhouse gas emissions and close the anthropogenic carbon loop. Recently, there has been intense interest in Cu2O-based catalysts for the CO2 reduction reaction (CO2RR), owing to their capabilities in enhancing C-C coupling. However, the electrochemical instability of Cu+ in Cu2O leads to its inevitable reduction to Cu0, resulting in poor selectivity for C2+ products. Herein, we propose an unconventional and feasible strategy for stabilizing Cu+ through the construction of a Ce4+ 4f-O 2p-Cu+ 3d network structure in Ce-Cu2O. Experimental results and theoretical calculations confirm that the unconventional orbital hybridization near Ef based on the high-order Ce4+ 4f and 2p can more effectively inhibit the leaching of lattice oxygen, thereby stabilizing Cu+ in Ce-Cu2O, compared with traditional d-p hybridization. Compared to pure Cu2O, the Ce-Cu2O catalyst increased the ratio of C2H4/CO by 1.69-fold during the CO2RR at -1.3 V. Furthermore, in situ and ex situ spectroscopic techniques were utilized to track the oxidation valency of copper under CO2RR conditions with time resolution, identifying the well-maintained Cu+ species in the Ce-Cu2O catalyst. This work not only presents an avenue to CO2RR catalyst design involving the high-order 4f and 2p orbital hybridization but also provides deep insights into the metal-oxidation-state-dependent selectivity of catalysts.

Modulating the Interfacial Water Network of Dual-Site Pd/FeOx/C Catalyst for Efficient Formate Electrooxidation.

The rational design of electrocatalysts for formate oxidation reaction (FOR) in alkaline media is crucial to promote the practical applications of direct formate fuel cells (DFFCs). The FOR kinetic on palladium (Pd) based electrocatalysts is strongly hindered by unfavorably adsorbed hydrogen (Had) as the major intermediate species blocking the active sites. Herein, we report a strategy of modulating the interfacial water network of dual-site Pd/FeOx/C catalyst to significantly enhance the desorption kinetics of Had during FOR. Aberration-corrected electron microscopy and synchrotron characterizations revealed the successful construction of Pd/FeOx interfaces on carbon support as a dual-site electrocatalyst for FOR. Electrochemical tests and in situ Raman spectroscopy results showed that Had could be effectively removed from the active sites of the as-designed Pd/FeOx/C catalyst. CO-stripping voltammetry and density functional theory calculations (DFT) demonstrated that the introduced FeOx could effectively accelerate the dissociative adsorption of water molecules on active sites, which accordingly generates adsorbed hydroxyl species (OHad) to facilitate the removal of Had during FOR. This work provides a novel route to develop advanced FOR catalysts for fuel cell applications.

Optimizing Electrocatalytic Nitrogen Reduction via Interfacial Electric Field Modulation: Elevating d-Band Center in WS2 -WO3 for Enhanced Intermediate Adsorption.

Electrocatalytic nitrogen reduction reaction (ENRR) has emerged as a promising approach to synthesizing green ammonia under ambient conditions. Tungsten (W) is one of the most effective ENRR catalysts. In this reaction, the protonation of intermediates is the rate-determining step (RDS). Enhancing the adsorption of intermediates is crucial to increase the protonation of intermediates, which can lead to improved catalytic performance. Herein, we constructed a strong interfacial electric field in WS2 -WO3 to elevate the d-band center of W, thereby strengthening the adsorption of intermediates. Experimental results demonstrated that this approach led to a significantly improved ENRR performance. Specifically, WS2 -WO3 exhibited a high NH3 yield of 62.38 µg h-1 mgcat -1 and a promoted faraday efficiency (FE) of 24.24 %. Furthermore, in situ characterizations and theoretical calculations showed that the strong interfacial electric field in WS2 -WO3 upshifted the d-band center of W towards the Fermi level, leading to enhanced adsorption of -NH2 and -NH intermediates on the catalyst surface. This resulted in a significantly promoted reaction rate of the RDS. Overall, our study offers new insights into the relationship between interfacial electric field and d-band center and provides a promising strategy to enhance the intermediates adsorption during the ENRR process.

Internal Electric Field Induced by Superexchange Interaction on Mn4+ -O2- -Ni2+ Unit Enables Highly Efficient Hybrid Capacitive Deionization.

Internal electric field (IEF) construction is an innovative strategy to regulate the electronic structure of electrode materials to promote charge transfer processes. Despite the wide use of IEF in various applications, the underlying mechanism of its formation in an asymmetric TM-O-TM unit still remains poorly understood. Herein, the essential principles for the IEF construction at electron occupancy state level and explore its effect on hybrid capacitive deionization (HCDI) performance is systematically investigated. By triggering a charge separation in Ni-MnO2 via superexchange interactions in a coordination structure unit of Mn4+ -O2- -Ni2+ , the formation of an IEF that can enhance charge transfer during the HCDI process is demonstrated. Experimental and theoretical results confirm the electrons transfer from O 2p orbital to TM (Ni2+ and Mn4+ ) eg orbital via superexchange interactions in the basic Mn4+ -O2- -Ni2+ coordination unit. As a result of the charge redistribution, the IEF endows Ni-MnO2 with superior electron and ion transfer property. This work presents a unique material design strategy that activates the electrochemical performance, and provides insights into the formation mechanism of IEF in an asymmetric TM-O-TM unit, which has potential applications in the construction of other innovative materials.

Enhanced Direct Electron Transfer Mediated Contaminant Degradation by Fe(IV) Using a Carbon Black-Supported Fe(III)-TAML Suspension Electrode System.

Iron complexes of tetra-amido macrocyclic ligands (Fe-TAML) are recognized to be effective catalysts for the degradation of a wide range of organic contaminants in homogeneous conditions with the high valent Fe(IV) and Fe(V) species generated on activation of the Fe-TAML complex by hydrogen peroxide (H2O2) recognized to be powerful oxidants. Electrochemical activation of Fe-TAML would appear an attractive alternative to H2O2 activation, especially if the Fe-TAML complex could be attached to the anode, as this would enable formation of high valent iron species at the anode and, importantly, retention of the valuable Fe-TAML complex within the reaction system. In this work, we affix Fe-TAML to the surface of carbon black particles and apply this "suspension anode" process to oxidize selected target compounds via generation of high valent iron species. We show that the overpotential for Fe(IV) formation is 0.17 V lower than the potential required to generate Fe(IV) electrochemically in homogeneous solution and also show that the stability of the Fe(IV) species is enhanced considerably compared to the homogeneous Fe-TAML case. Application of the carbon black-supported Fe-TAML suspension anode reactor to degradation of oxalate and hydroquinone with an initial pH value of 3 resulted in oxidation rate constants that were up to three times higher than could be achieved by anodic oxidation in the absence of Fe-TAML and at energy consumptions per order of removal substantially lower than could be achieved by alternate technologies.

Electrochemical Reduction of Nitrate with Simultaneous Ammonia Recovery Using a Flow Cathode Reactor.

The presence of excessive concentrations of nitrate in industrial wastewaters, agricultural runoff, and some groundwaters constitutes a serious issue for both environmental and human health. As a result, there is considerable interest in the possibility of converting nitrate to the valuable product ammonia by electrochemical means. In this work, we demonstrate the efficacy of a novel flow cathode system coupled with ammonia stripping for effective nitrate removal and ammonia generation and recovery. A copper-loaded activated carbon slurry (Cu@AC), made by a simple, low-cost wet impregnation method, is used as the flow cathode in this novel electrochemical reactor. Use of a 3 wt % Cu@AC suspension at an applied current density of 20 mA cm-2 resulted in almost complete nitrate removal, with 97% of the nitrate reduced to ammonia and 70% of the ammonia recovered in the acid-receiving chamber. A mathematical kinetic model was developed that satisfactorily describes the kinetics and mechanism of the overall nitrate electroreduction process. Minimal loss of Cu to solution and maintenance of nitrate removal performance over extended use of Cu@AC flow electrode augers well for long-term use of this technology. Overall, this study sheds light on an efficient, low-cost water treatment technology for simultaneous nitrate removal and ammonia generation and recovery.

Hydroxyl radicals in anodic oxidation systems: generation, identification and quantification.

Anodic oxidation has emerged as a promising treatment technology for the removal of a broad range of organic pollutants from wastewaters. Hydroxyl radicals are the primary species generated in anodic oxidation systems to oxidize organics. In this review, the methods of identifying hydroxyl radicals and the existing debates and misunderstandings regarding the validity of experimental results are discussed. Consideration is given to the methods of quantification of hydroxyl radicals in anodic oxidation systems with particular attention to approaches used to compare the electrochemical performance of different anodes. In addition, we describe recent progress in understanding the mechanisms of hydroxyl radical generation at the surface of most commonly used anodes and the utilization of hydroxyl radical in typical electrochemical reactors. This review shows that the key challenges facing anodic oxidation technology are related to i) the elimination of mistakes in identifying hydroxyl radicals, ii) the establishment of an effective hydroxyl radical quantification method, iii) the development of cost effective anode materials with high corrosion resistance and high electrochemical activity and iv) the optimization of electrochemical reactor design to maximise the utilization efficiency of hydroxyl radicals.

Integrated flow anodic oxidation and ultrafiltration system for continuous defluorination of perfluorooctanoic acid (PFOA).

While flow anodic oxidation systems can efficiently generate hydroxyl radicals (·OH) and significantly enhance direct electron transfer (DET) processes that result in the oxidation of target contaminants via the charge percolating network of flow anode particles, challenges remain in constructing a flow anodic oxidation system that can be operated continuously with stable performance. Here we incorporate an ultrafiltration (UF) membrane module into the flow anodic oxidation system and achieve the continuous defluorination of perfluorooctanoic acid (PFOA) for 12 days with high efficiency (94.1%) and reasonable energy consumption (38.1 Wh mg-1) compared to other advanced oxidation processes by using a mixture of conducting TixO2x-1 and Pd/CNT particles as the flow anode. The results indicate that DET, ·OH mediated oxidation and adsorption processes play critical roles in the degradation of PFOA during the flow anodic oxidation processes. The synergistic effect of the TixO2x-1 and Pd/CNT particles enhances the defluorination efficiency by 3.2 times at 4.5 V vs Ag/AgCl compared to the control experiment (no flow anode particles present) and promotes the release of F- into solution while other intermediate products remain adsorbed to the surface of the Pd/CNT particles. Although the Pd/CNT particles were oxidized after the long-term operation, no obvious Pd ion leakage into solution was observed. Results of this study support the feasibility of continuous operation of a flow anode/UF system with stable performance and pave the way for the translation of this advanced oxidation technology to practical application.

Direct electron transfer (DET) processes in a flow anode system-Energy-efficient electrochemical oxidation of phenol.

In flow anode systems, surface-bound hydroxyl radicals (*OH) are generated at the solid-liquid interface of suspended particulate charge carriers at potentials well below that required for oxygen evolution as a result of water splitting. While these surface-bound radicals are powerful indiscriminant oxidants that often lead to complete mineralization of organic pollutants, the more selective process of direct electron transfer (DET) may also occur at the particle electrode interfaces and play a critical role in the degradation of some contaminants. In this study, we investigated DET processes in a flow anode system in which carbon black was utilized as the flow anode material and Pt, Ti, IrRu and IrTa meshes were used as the current collectors. The results indicate that the use of a carbon black flow anode enhanced the DET rate by 20 times at 1.0 V vs Ag/AgCl compared to the control experiment with no carbon black particles present. Low solution conductivity had a more obvious negative effect on the DET process (compared to *OH mediated oxidation) due to the high potential drop and inhibition of mass transfer processes at the solid-liquid interfaces of the anode particles. The DET rates were dependent on the particular anode current collector used (i.e., Ti, IrRu, IrTa or Pt mesh) with differences in rates ascribed to the electron transfer resistance of the current collectors in the flow anode system. Detailed investigation of the degradation of phenol in a flow anode system revealed that this widely studied contaminant could be degraded with an energy consumption of 3.08 kWh m-3, a value substantially lower than that required with other techniques. Results of this study provide a better understanding of the DET mechanism at the solid-solid and solid-liquid interfaces with these insights expected to benefit the design of flow anode materials and current collectors and lead to the improvement in performance of flow anode systems.

Flow anodic oxidation: Towards high-efficiency removal of aqueous contaminants by adsorbed hydroxyl radicals at 1.5 V vs SHE.

Electrochemical advanced oxidation processes (EAOPs) have emerged as a promising water treatment alternative but major breakthroughs are still needed in order for EAOPs to be competitive with traditional treatment technologies in terms of energy cost. Most existing studies have been conducted at high potentials to generate the powerful hydroxyl radical oxidant (aqueous •OH). While adsorbed hydroxyl radicals (OH*) may form at a much lower energy cost, their possible utilization is limited due to the poor mass transfer of this highly reactive species on solid electrodes. In this report, we describe a novel flow anode system using 4-16 µm Magnéli phase titanium suboxide particles as the anode material which enables the generation of a high steady state •OH concentration (5.4 × 10-12 mol m-2) at only 1.5 V (vs SHE) in a dilute electrolyte (5 mM KH2PO4). The energy cost of removal per order of selected water contaminants (tetracycline and orange II in this study) using the flow anode is 1.5--6.7 Wh m-3, which is 1 - 4 orders of magnitude lower than that of existing techniques. The anode material used demonstrates great stability with the configuration readily scaled up. The results of this study provide new insight into a high efficiency, low cost water treatment technology for organic contaminant degradation.

Effect of the Presence of Carbon in Ti4O7 Electrodes on Anodic Oxidation of Contaminants.

Magnéli phase titanium suboxide, Ti4O7, has attracted increasing attention as a potential electrode material in anodic oxidation as a result of its high efficiency and (electro)chemical stability. Although carbon materials have been amended to Ti4O7 electrodes to enhance the electrochemical performance or are present as an unwanted residual during the electrode fabrication, there has been no comprehensive investigation of how these carbon materials affect the electrochemical performance of the resultant Ti4O7 electrodes. As such, we investigated the electrochemical properties of Ti4O7 electrodes impregnated with carbon materials at different contents (and chemical states). Results of this study showed that while pure Ti4O7 electrodes exhibited an extremely low rate of interfacial electron transfer, the introduction of minor amounts of carbon materials (at values as low as 0.1 wt %) significantly facilitated the electron transfer process and decreased the oxygen evolution reaction potential. The oxygen-containing functional groups have been shown to play an important role in interfacial electron transfer with moderate oxidation of the carbon groups aiding electron uptake at the electrode surface (and consequently organic oxidation) while the generation of carboxyl groups-a process that is likely to occur in long-term operation-increased the interfacial resistance and thus retarded the oxidation process. Results of this study provide a better understanding of the relationship between the nature of the electrode surface and anodic oxidation performance with these insights likely to facilitate improved electrode design and optimization of operation of anodic oxidation reactors.