Improved Operation of Chloralkaline Reversible Cells with Mixed Metal Oxide Electrodes Made Using Microwaves

This study focuses on the synthesis of mixed metal oxide anodes (MMOs) with the composition Ti/RuO2Sb2O4Ptx (where x = 0, 5, 10 mol) using hybrid microwave irradiation heating. The synthesized electrodes were characterized using scanning electron microscopy, X-ray energy-dispersive analysis, X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy. These electrodes were then evaluated in both bulk electrolytic and fuel cell tests within a reversible chloralkaline electrochemical cell. The configurations using the electrodes Ti/(RuO2)0.7-(Sb2O4)0.3 and Ti/(RuO2)66.5-(Sb2O4)28.5-Pt5 presented lower onset potential for oxygen and chlorine evolution reactions and reduced resistance to charge transfer compared to the Ti/(RuO2)63-(Sb2O4)27-Pt10 variant. These electrodes demonstrated notable performance in reversible electrochemical cells, achieving Coulombic efficiencies of up to 60% when operating in the electrolytic mode at current densities of 150 mA cm-2. They also reached maximum power densities of 1.2 mW cm-2 in the fuel cell. In both scenarios, the presence of platinum in the MMO coating positively influenced the process. Furthermore, a significant challenge encountered was crossover through the membranes, primarily associated with gaseous Cl2. This study advances our understanding of reversible electrochemical cells and presents possibilities for further exploration and refinement. It demonstrated that the synergy of innovative electrode synthesis strategies and electrochemical engineering can lead to promising and sustainable technologies for energy conversion.

Boosting Ammonium Oxidation in Wastewater by the BiOCl-Functionalized Anode

Mixed metal oxide (MMO) anodes are commonly used for electrochlorination of ammonium (NH4+) in wastewater treatment, but they suffer from low efficiency due to inadequate chlorine generation at low Cl- concentrations and sluggish reaction kinetics between free chlorine and NH4+ under acidic pH conditions. To address this challenge, we develop a straightforward wet chemistry approach to synthesize BiOCl-functionalized MMO electrodes using the MMO as an efficient Ohmic contact for electron transfer. Our study demonstrates that the BiOCl@MMO anode outperforms the pristine MMO anode, exhibiting higher free chlorine generation (24.6-60.0 mg Cl2 L-1), increased Faradaic efficiency (75.5 vs 31.0%), and improved rate constant of NH4+ oxidation (2.41 vs 0.76 mg L-1 min-1) at 50 mM Cl- concentration. Characterization techniques including electron paramagnetic resonance and in situ transient absorption spectra confirm the production of chlorine radicals (Cl• and Cl2•-) by the BiOCl/MMO anode. Laser flash photolysis reveals significantly higher apparent second-order rate constants ((4.3-4.9) × 106 M-1 s-1 at pH 2.0-4.0) for the reaction between NH4+ and Cl•, compared to the undetectable reaction between NH4+ and Cl2•-, as well as the slower reaction between NH4+ and free chlorine (102 M-1 s-1 at pH < 4.0) within the same pH range, emphasizing the significance of Cl• in enhancing NH4+ oxidation. Mechanistic studies provide compelling evidence of the capacity of BiOCl for Cl- adsorption, facilitating chlorine evolution and Cl• generation. Importantly, the BiOCl@MMO anode exhibits excellent long-term stability and high catalytic activity for NH4+-N removal in a real landfill leachate. These findings offer valuable insights into the rational design of electrodes to improve electrocatalytic NH4+ abatement, which holds great promise for wastewater treatment applications.

Preparation and Photovoltaic Evaluation of CuO@Zn(Al)O-Mixed Metal Oxides for Dye Sensitized Solar Cell

In this manuscript, a series of dye-sensitized solar cells (DSSCs) were fabricated as a function of post-processing temperature based on mesoporous CuO@Zn(Al)O-mixed metal oxides (MMO) in conjunction with dye N719 as the main light absorber; the proposed CuO@Zn(Al)O geometry was, in turn, attained using Zn/Al-layered double hydroxide (LDH) as a precursor via combination of co-precipitation and hydrothermal techniques. In particular, the dye loading amount onto the deposited mesoporous materials was anticipated via regression equation-based UV-Vis technique analysis, which evidently demonstrated a robust correlation along with the fabricated DSSCs power conversion efficiency. In detail, of the DSSCs assembled, CuO@MMO-550 exhibited short-circuit current (JSC) and open-circuit voltage (VOC) of 3.42 (mA/cm²) and 0.67 (V) which result in significant fill factor and power conversion efficiency of 0.55% and 1.24%, respectively. This could mainly be due to the relatively high surface area of 51.27 (m²/g) which in turn validates considerable dye loading amount of 0.246 (mM/cm^-2).

Creating Highly Active Iron Sites in Electrochemical N2 Reduction by Fabricating Strongly-Coupled Interfaces

Electrochemical N_c reduction has been regarded as one of the most promising approaches to producing ammonia under mild conditions, but there are remaining pressing challenges in improving the reaction rate and efficiency. Herein, an unconventional galvanic replacement reaction is reported to fabricate a unique hierarchical structure composed of Fe₃ O₄ -CeO₂ bimetallic nanotubes covered by Fe₂ O₃ ultrathin nanosheets. Control experiments reveal that CeO₂ species play the essential role of stabilizer for Fe²⁺ cations. Compared with bare CeO₂ and Fe₂ O₃ nanotubes, the as-obtained Fe₂ O₃ /Fe₃ O₄ -CeO₂ possesses a remarkably enhanced NH₃ yield rate (30.9 µg h^-1 mg_cat ^-1 ) and Faradaic efficiency (26.3%). The enhancement can be attributed to the hierarchical feature that makes electrodes more easily to contact with electrolytes. More importantly, as verified by density functional theory calculations, the generation of Fe₂ O₃ -Fe₃ O₄ heterogeneous junctions can efficiently optimize the reaction pathways, and the energy barrier of the potential determining step (the *N₂ hydrogenates into *N*NH) is significantly decreased.

Facile Synthesis of Silane-Modified Mixed Metal Oxide as Catalyst in Transesterification Processes

The fast depletion of fossil fuels has attracted researchers worldwide to explore alternative biofuels, such as biodiesel. In general, the production of biodiesel is carried out via transesterification processes of vegetable oil with the presence of a suitable catalyst. A mixed metal oxide has shown to be a very attractive heterogeneous catalyst with a high performance. Most of the mixed metal oxide is made by using the general wetness impregnation method. A simple route to synthesize silane-modified mixed metal oxide (CaO-CuO/C6) catalysts has been successfully developed. A fluorocarbon surfactant and triblock copolymers (EO)106(PO)70(EO)106 were used to prevent the crystal agglomeration of carbonate salts (CaCO3-CuCO3) as the precursor to form CaO-CuO with a definite size and morphology. The materials show high potency as a catalyst in the transesterification process to produce biodiesel. The calcined co-precipitation product has a high crystallinity form, as confirmed by the XRD analysis. The synthesized catalyst was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX). The mechanism of surface modification and the effects of the catalytic activity were also discussed. The biodiesel purity of the final product was analyzed by gas chromatography. The optimum biodiesel yield was 90.17% using the modified mixed metal oxide CaO-CuO/C6.

[Preparation of Mixed Metal Oxide/Carbon Composites and Its Adsorption Performance for Pb(Ⅱ)]

Layered double hydroxides, which can be synthesized from metal ions and their analogs, have abundant interlayer ions, surface functional groups, and adsorption characteristics that have been extensively studied. But the adsorption-desorption process may cause secondary pollution of the environment. In this study, the layered double hydroxides that adsorbed Congo red were converted into mixed metal oxide/carbon composites by a calcining carbonization method, and its adsorption performance for heavy metal ions Pb(Ⅱ) in aqueous solution was studied in detail. The results show that the prepared mixed metal oxide/carbon composites have a faster adsorption rate and higher adsorption capacity for Pb(Ⅱ). The adsorption capacity reached more than 150 mg·g^-1 in 30 min, and increased with the content of Mg²⁺ introduced into the layered double metal hydroxide, reaching a maximum of 368 mg·g^-1. The removal mechanism of Pb(Ⅱ) by mixed metal oxide/carbon composites was caused by the formation of insoluble Pb₃(CO₃) ₂(OH) ₂ on the surface. This research lays the foundation for the application of mixed metal oxide/carbon composites in the remediation of lead-containing soils.

A Facile Synthesis of NiFe-Layered Double Hydroxide and Mixed Metal Oxide with Excellent Microwave Absorption Properties

Microwave-absorbing materials have attracted increased research interest in recent years because of their core roles in the fields of electromagnetic (EM) pollution precaution and information security. In this paper, microwave-absorbing material NiFe-layered double hydroxide (NiFe-LDH) was synthesized by a simple co-precipitation method and calcined for the fabrication of NiFe-mixed metal oxide (NiFe-MMO). The phase structure and micromorphology of the NiFe-LDH and NiFe-MMO were analyzed, and their microwave-absorbing properties were investigated with a vector network analyzer in 2–18 GHz. Both NiFe-LDH and NiFe-MMO possessed abundant interfaces and a low dielectric constant, which were beneficial to electromagnetic wave absorption, owing to the synergistic effect of multi-relaxation and impedance matching. The optimum reflection loss (RL) of NiFe-LDH and NiFe-MMO was −58.8 dB and −64.4 dB, respectively, with the thickness of 4.0 mm in the C band. This work demonstrates that LDH-based materials have a potential application in electromagnetic wave absorption.

Mixed Metal Oxide by Calcination of Layered Double Hydroxide: Parameters Affecting Specific Surface Area

Mixed metal oxide (MMO) is one of the widely utilized ceramic materials in various industries. In order to obtain high performance, the specific surface area of MMO should be controlled. Calcination of layered double hydroxide (LDH) is a versatile way to prepare MMO with homogeneous metal distribution and well-developed porosity. Although researchers found that the specific surface area of LDH-originated MMO was relatively high, it had not been systematically investigated how the surface area is controlled under a certain parameter. In this review, we summarized LDH-originated MMO with various starting composition, calcination temperature, and pore developing agent in terms of specific surface area and porosity. Briefly, it was represented that MMOs with Mg-Al components generally had higher specific surface area than Mg-Fe or Zn-Al components. Calcination temperature in the range 300–600 °C resulted in the high specific surface area, while upper or lower temperature reduced the values. Pore developing agent did not result in dramatic increase in MMO; however, the pore size distribution became narrower in the presence of pore developing agents.

Development of Mesopore Structure of Mixed Metal Oxide through Albumin-Templated Coprecipitation and Reconstruction of Layered Double Hydroxide

Mixed metal oxide (MMO) with relatively homogeneous mesopores was successfully obtained by calcination and reconstruction of albumin-templated layered double hydroxide (LDH). The aggregation degree of albumin-template was controlled by adjusting two different synthesis routes, coprecipitation and reconstruction. X-ray diffraction patterns and scanning electron microscopic images indicated that crystal growth of LDH was fairly limited during albumin-templated coprecipitation due to the aggregation. On the hand, crystal growth along the lateral direction was facilitated in albumin-templated reconstruction due to the homogeneous distribution of proteins moiety. Different state of albumin during LDH synthesis influenced the local disorder and porous structure of calcination product, MMO. The N₂ adsorption-desorption isotherms demonstrated that calcination on reconstructed LDH produced MMO with large specific surface area and narrow distribution of mesopores compared with calcination of coprecipitated LDH.

Efficient Electrochemical Oxygen Reduction to Hydrogen Peroxide by Transition Metal-Doped Silicate Sr0.7Na0.3SiO3-δ

Electrochemical oxygen reduction in a selective two-electron pathway is an efficient method for onsite production of H₂O₂. State of the art noble metal-based catalysts will be prohibitive for widespread applications, and hence earth-abundant oxide-based systems are most desired. Here we report transition metal (Mn, Fe, Ni, Cu)-doped silicates, Sr_0.7Na_0.3SiO_3-δ, as potential electrocatalysts for oxygen reduction to H₂O₂ in alkaline conditions. These novel compounds are isostructural with the parent Sr_0.7Na_0.3SiO_3-δ and crystallize in monoclinic structure with corner-shared SiO₄ groups forming cyclic trimers. The presence of Na stabilizes O vacancies created on doping, and the transition metal ions provide catalytically active sites. Electrochemical parameters estimated from Tafel and Koutechy-Levich plots suggest a two-electron transfer mechanism, indicating peroxide formation. This is confirmed by the rotating ring disc electrode method, and peroxide selectivity and Faradaic efficiency are calculated to be in the range of 65-82% and 50-68%, respectively, in a potential window 0.3 to 0.6 V (vs RHE). Of all the dopants, Ni imparts the maximum selectivity and efficiency as well as highest rate of formation of H₂O₂ at 1.65 μmol s^-1.

Accelerated Life Testing of a Palladium-Doped Tin Oxide Electrode for Zn Electrowinning

Electrowinning is a technique that can be used to obtain high-purity elements through electrolysis. The degradation of accelerated life testing for Pd-based electrodes is discussed in this study. The lifetime of the electrodes was examined by multiplying the acceleration rate with the current to measure the voltage of the electrodes. The acceleration rate was set to 10, 20, and 30 times. Four components were deposited on the TiO₂ plate. The ratio of Ir to Sn was fixed at 1:1, while Ta was deposited at 10 wt.%. Pd was deposited at 2, 4, 8 and 10 wt.% to create Pd-Ir/Sn-Ta. The initial voltage decreased as the Pd deposition amount increased irrespective of the acceleration rate. The lower the acceleration rate, the lower the voltage. An increase in the Pd content caused the initial voltage to be low. The multiple of the acceleration rate slightly increased for all cases of life testing for one year. When the test was conducted by increasing the current density by 20 times, the increase in voltage was proportional to the Pd deposition amount. However, for the 30 times acceleration rate, the lifetime of the electrodes was shortened as the Pd content increased. It can be inferred that the content of Pd and the ratio of Ir to Sn can influence the lifetime of the electrodes. According to these results, if the multiple of the acceleration rate is too extreme, the lifetime of the electrodes cannot be evaluated because they are damaged in an extreme situation.

Solar-Driven H2 O2 Generation From H2 O and O2 Using Earth-Abundant Mixed-Metal Oxide@Carbon Nitride Photocatalysts

Light-driven generation of H2 O2 only from water and molecular oxygen could be an ideal pathway for clean production of solar fuels. In this work, a mixed metal oxide/graphitic-C3 N4 (MMO@C3 N4 ) composite was synthesized as a dual-functional photocatalyst for both water oxidation and oxygen reduction to generate H2 O2 . The MMO was derived from a NiFe-layered double hydroxide (LDH) precursor for obtaining a high dispersion of metal oxides on the surface of the C3 N4 matrix. The C3 N4 is in the graphitic phase and the main crystalline phase in MMO is cubic NiO. The XPS analyses revealed the doping of Fe(3+) in the dominant NiO phase and the existence of surface defects in the C3 N4 matrix. The formation and decomposition kinetics of H2 O2 on the MMO@C3 N4 and the control samples, including bare MMO, C3 N4 matrix, Ni- or Fe-loaded C3 N4 and a simple mixture of MMO and C3 N4 , were investigated. The MMO@C3 N4 composite produced 63 μmol L(-1) of H2 O2 in 90 min in acidic solution (pH 3) and exhibited a significantly higher rate of production for H2 O2 relative to the control samples. The positive shift of the valence band in the composite and the enhanced water oxidation catalysis by incorporating the MMO improved the light-induced hole collection relative to the bare C3 N4 and resulted in the enhanced H2 O2 formation. The positively shifted conduction band in the composite also improved the selectivity of the two-electron reduction of molecular oxygen to H2 O2 .

Semi-Coke-Supported Mixed Metal Oxides for Hydrogen Sulfide Removal at High Temperatures

To improve the desulfurization efficiency of sorbents at low cost, modified semi-coke was used as the substrate for mixed metal oxides (ZFM; oxides of zinc [Zn], iron [Fe], and manganese [Mn]) in hot gas desulfurization. Performance of the prepared ZFM/modified semi-coke (MS) sorbents were evaluated in a fixed-bed reactor in the temperature range 400-550°C. Results showed that the molar ratio of Mn to Zn, effect of the substrate, the calcination temperature, and the sulfidation temperature influenced the performance of the sorbents. Optimum conditions for the preparation of the ZFM/MS sorbents were molar ratio of Mn(NO(3))(2)·6H(2)O, Zn(NO(3))(2), and Fe(NO(3))(3), 0.6:1:2; mass ratio of ZFM0.6 to modified semi-coke support, 1:1; and calcination temperature, 600°C. The ZFM0.6/MS sorbent thus prepared exhibited the best sorption sulfur capacity of 27.46% at 450°C.