RESUMEN

Prussian blue analogues (PBA) are a large family of functional materials with diverse applications such as in electrochemical fields. However, their use in the emerging two-electron oxygen reduction reaction for clean production of hydrogen peroxide (H2O2) is lagging. Herein, a general solvent exchange induced reconstruction strategy is demonstrated, through which an abnormal NiNi-PBA superstructure is synthesized as a high-performance electrocatalyst for H2O2 generation. The resultant NiNi-PBA superstructure has a stoichiometric composition with saturated lattice water, and a leaf-like morphology composed of interconnected small-size nanosheets with identical orientation and predominate {210} side surface exposure. Our studies show that the Ni-N centers on {210} facets are the active sites, and the saturated lattice H2O favors a six-coordinated environment that results in high selectivity. The "perfect" structure including stoichiometric composition and ideal facet exposure leads to a high selectivity of ~100% and H2O2 yield of 5.7 mol g-1 h-1, superior to the reported MOF-based electrocatalysts and most other electrocatalysts.

RESUMEN

Electrochemical synthesis of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e--ORR) provides an alternative method to the energy-intensive anthraquinone method. Metal macrocycles with precise coordination are widely used for 2e--ORR electrocatalysis, but they have to be commonly loaded on conductive substrates, thus exposing a large number of 2e--ORR-inactive sites that result in poor H2O2 production rate and efficiency. Herein, guided by first-principle predictions, a substrate-free and two-dimensional conductive metal-organic framework (Ni-TCPP(Co)), composed of Co-N4 sites in porphine(Co) centers and Ni2O8 nodes, is designed as a multi-site catalyst for H2O2 electrosynthesis. The approperiate distance between the CoN4 and Ni2O8 sites in Ni-TCPP(Co) weakens the electron transfer between them, thus ensuring their inherent activities and creating high-density active sites. Meanwhile, the intrinsic electronic conductivity and porosity of Ni-TCPP(Co) further facilitate rapid reaction kinetics. Therefore, outstanding 2e--ORR electrocatalytic performance has been achieved in both alkaline and neutral electrolytes (>90%/85% H2O2 selectivity within 0-0.8 V vs. RHE and >18.2/18.0 mol g-1 h-1 H2O2 yield under alkaline/neutral conditions), with confirmed feasibility for water purification and disinfection applications. This strategy thus provides a new avenue for designing catalysts with precise coordination and high-density active sites, promoting high-efficiency electrosynthesis of H2O2 and beyond.

RESUMEN

In the Electro-Fenton (EF) process, hydrogen peroxide (H2O2) is produced in situ by a two-electron oxygen reduction reaction (2e ORR), which is further activated by electrocatalysts to generate reactive oxygen specieces (ROS). However, the selectivity of 2e transfer from catalysts to O2 is still unsatisfactory, resulting in the insufficient H2O2 availability. Carbon based materials with abundant oxygen-containing functional groups have been used as excellent 2e ORR electrocatalysts, and atomic hydrogen (H*) can quickly transfer one electron to H2O2 in a wide pH range and avoiding the restrict of traditional Fenton reaction. Herein, nickel nanoparticles growth on oxidized carbon deposited on modified carbon felt (Ni/Co@CFAO) was prepared as a bifunctional catalytic electrode coupling 2e ORR to form H2O2 with H* reducing H2O2 to produce ROS for highly efficient degradation of antibiotics. Electrochemical oxidation and thermal treatment were used to modulate the structure of carbon substrates for increasing the electro-generation of H2O2, while H* was produced over Ni sites through H2O/H+ reduction constructing an in-situ EF system. The experimental results indicated that 2e ORR and H* induced EF processes could promote each other mutually. The optimized Ni/Co@CFAO with a Ni:C mass ratio of 1:9 exhibited a high 2e selectivity and H2O2 yield of 49 mg L-1. As a result, the designed Ni/Co@CFAO exhibited excellent electrocatalytic ability to degrade tetracycline (TC) under different aqueous environmental conditions, and achieved 98.5% TC removal efficiency within 60 min H2O2 and H* were generated simultaneously at the bifunctional cathode and react to form strong oxidizing free radicals •OH. At the same time, O2 gained an electron to form •O2-, which could react with •OH and H2O to form 1O2, which had relatively long life (10-6∼10-3 s), further promoting the efficient removal of antibiotics in water.

RESUMEN

Hydrogen peroxide (H2O2) plays a pivotal role in advancing sustainable technologies due to its eco-friendly oxidizing capability. The electrochemical two-electron (2e-) oxygen reduction reaction and water oxidation reaction present an environmentally green method for H2O2 production. Over the past three years, significant progress is made in the field of carbon-based metal-free electrochemical catalysts (C-MFECs) for low-cost and efficient production of H2O2 (H2O2EP). This article offers a focused and comprehensive review of designing C-MFECs for H2O2EP, exploring the construction of dual-doping configurations, heteroatom-defect coupling sites, and strategic dopant positioning to enhance H2O2EP efficiency; innovative structural tuning that improves interfacial reactant concentration and promote the timely release of H2O2; modulation of electrolyte and electrode interfaces to support the 2e- pathways; and the application of C-MFECs in reactors and integrated energy systems. Finally, the current challenges and future directions in this burgeoning field are discussed.

RESUMEN

The two-electron electrocatalytic oxygen reduction reaction (ORR) to hydrogen peroxide (H2O2) is a valuable alternative to the more conventional and energy-intensive anthraquinone process. From a circularity viewpoint, metal-free catalysts constitute a sustainable alternative for the process. In particular, lightweight hetero-doped C-materials are cost-effective and easily scalable samples that replace - more and more frequently - the use of critical raw elements in the preparation of highly performing (electro)catalysts. Anyhow, their large-scale exploitation in industrial processes still suffers from technical limits of samples upscale and reproducibility other than a still moderate comprehension of their action mechanism in the process. This concept article offers a comprehensive and exhaustive "journey" through the most representative lightweight hetero-doped C-based electrocatalysts and their performance in the 2e- ORR process. It provides an interpretation of phenomena at the triple-phase interface of solid catalyst, liquid electrolyte and gaseous oxygen based on the doping-driven generation of ideal electronic microenvironments at the catalyst surface.

RESUMEN

Direct electrosynthesis of hydrogen peroxide (H2O2) with high production rate and high selectivity through the two-electron oxygen reduction reaction (2e-ORR) offers a sustainable alternative to the energy-intensive anthraquinone technology but remains a challenge. Herein, a low-coordinated, 2D conductive Zn/Cu metal-organic framework supported on hollow nanocube structures (ZnCu-MOF (H)) is rationally designed and synthesized. The as-prepared ZnCu-MOF (H) catalyst exhibits substantially boosted electrocatalytic kinetics, enhanced H2O2 selectivity, and ultra-high Faradaic efficiency for 2e-ORR process in both alkaline and neutral conditions. Electrochemical measurements, operando/quasi in situ spectroscopy, and theoretical calculation demonstrate that the introduction of Cu atoms with low-coordinated structures induces the transformation of active sites, resulting in the beneficial electron transfer and the optimized energy barrier, thereby improving the electrocatalytic activity and selectivity.

RESUMEN

Two-electron oxygen reduction reaction (2e- ORR) is a promising method for the synthesis of hydrogen peroxide (H2O2). However, high energy barriers for the generation of key *OOH intermediates hinder the process of 2e- ORR. Herein, we prepared a copper-supported indium selenide catalyst (Cu/In2Se3) to enhance the selectivity and yield of 2e- ORR by employing an electronic metal-support interactions (EMSIs) strategy. EMSIs-induced charge rearrangement between metallic Cu and In2Se3 is conducive to *OOH intermediate generation, promoting H2O2 production. Theoretical investigations reveal that the inclusion of Cu significantly lowers the energy barrier of the 2e- ORR intermediate and impedes the 4e- ORR pathway, thus favoring the formation of H2O2. The concentration of H2O2 produced by Cu/In2Se3 is ~2 times than In2Se3, and Cu/In2Se3 shows promising applications in antibiotic degradation. This research presents a valuable approach for the future utilization of EMSIs in 2e- ORR.

RESUMEN

Understanding selectivity trends is a crucial hurdle in the developing innovative catalysts for generating hydrogen peroxide through the two-electron oxygen reduction reaction (2e-ORR). The identification of selectivity patterns has been made more accessible through the introduction of a newly developed selectivity descriptor derived from thermodynamics, denoted as ΔΔG introduced in Chem Catal. 2023, 3(3), 100568. To validate the suitability of this parameter as a descriptor for 2e-ORR selectivity, we utilize an extensive library of 155 binary alloys. We validate that ΔΔG reliably depicts the selectivity trends in binary alloys reported for their high activity in the 2e-ORR. This analysis also enables the identification of nine selective 2e-ORR catalysts underscoring the efficacy of ΔΔG as 2e-ORR selectivity descriptor. This work highlights the significance of concurrently considering both selectivity and activity trends. This holistic approach is crucial for obtaining a comprehensive understanding in the identification of high-performance catalyst materials for optimal efficiency in various applications.

RESUMEN

Developing stable and highly selective two-electron oxygen reduction reaction (2e- ORR) electrocatalysts for producing hydrogen peroxide (H2 O2 ) is considered a major challenge to replace the anthraquinone process and achieve a sustainable green economy. Here, we doped Sn into Ti4 O7 (D-Sn-Ti4 O7 ) by simple polymerization post-calcination method as a high-efficiency 2e- ORR electrocatalyst. In addition, we also applied plain calcination after the grinding method to load Sn on Ti4 O7 (L-Sn-Ti4 O7 ) as a comparison. However, the performance of L-Sn-Ti4 O7 is far inferior to that of the D-Sn-Ti4 O7 . D-Sn-Ti4 O7 exhibits a starting potential of 0.769 V (versus the reversible hydrogen electrode, RHE) and a high H2 O2 selectivity of 95.7 %. Excitingly, the catalyst can maintain a stable current density of 2.43 mA ⋅ cm-2 for 3600 s in our self-made H-type cell, and the cumulative H2 O2 production reaches 359.2 mg ⋅ L-1 within 50,000 s at 0.3 V. The performance of D-Sn-Ti4 O7 is better than that of the non-noble metal 2e- ORR catalysts reported so far. The doping of Sn not only improves the conductivity but also leads to the lattice distortion of Ti4 O7 , further forming more oxygen vacancies and Ti3+ , which greatly improves its 2e- ORR performance compared with the original Ti4 O7 . In contrast, since the Sn on the surface of L-Sn-Ti4 O7 displays a synergistic effect with Tin+ (3≤n≤4) of Ti4 O7 , the active center Tin+ dissociates the O=O bond, making it more inclined to 4e- ORR.

RESUMEN

The improvement of electrochemiluminescence (ECL) intensity in luminol, a classic electrochemiluminescent material, remains a controversial topic. In this study, synthesis of acetylene black oxide (ACETO) through simple air annealing was successful in introducing oxygen-containing groups and defects, which can act as active sites for the oxygen reduction reaction (ORR) and exhibit excellent catalytic activity. By introducing the two-electron (2e-) ORR into the cathode ECL system of luminol, integration of ACETO and luminol allows for in situ generation of dissolved oxygen into reactive oxygen species (ROS), thereby enhancing the ECL intensity of luminol. It is worth noting that iron-nitrogen-carbon (FeNC), as a secondary antibody (Ab2) label, can catalyze the decomposition of H2O2, the product of 2e- ORR, into ROS to achieve ECL amplification. Alpha-fetoprotein (AFP), an important tumor marker, was successfully detected with a detection limit of 0.01 pg/mL, indicating that this ECL signal amplification strategy has broad application prospects in biological analysis.

Asunto(s)

Técnicas Biosensibles , Nanopartículas del Metal , Luminol/química , Peróxido de Hidrógeno , Especies Reactivas de Oxígeno , Temperatura , Nanopartículas del Metal/química , Mediciones Luminiscentes , Técnicas Electroquímicas , Electrodos , Límite de Detección , Alquinos

RESUMEN

Heterogeneous electro-Fenton (HEF) process has been regarded as a promising method in environmental remediation. However, the reaction kinetic mechanism of the HEF catalyst for simultaneous production and activation of H2O2 remained confounded. Herein, the copper supported on polydopamine (Cu/C) was synthesized by a facile method and employed as a bifunctional HEFcatalyst, and the catalytic kinetic pathways were deeply investigated by using rotating ring-disk electrode (RRDE) voltammetry based on the Damjanovic model. Experimental results substantiated that a two-electron oxygen reduction reaction (2e- ORR) and a sequential Fenton oxidation reaction were proceeded on 1.0-Cu/C, where metallic copper played a crucial role in the fabrication of 2e- active sites as well as utmost H2O2 activation to produce highly reactive oxygen species (ROS), resulting in the high H2O2 productivity (52.2%) and the almost complete removal of contaminant ciprofloxacin (CIP) after 90 min. The work not only expanded the idea of reaction mechanism on Cu-based catalyst in HEF process but also provided a promising catalyst for pollutants degradation in wastewater treatment.

Asunto(s)

Cobre , Contaminantes Químicos del Agua , Cobre/química , Peróxido de Hidrógeno/química , Contaminantes Químicos del Agua/análisis , Indoles , Catálisis , Oxidación-Reducción , Electrodos

RESUMEN

Electrochemical two-electron oxygen reduction reaction (2 e- ORR) to produce hydrogen peroxide (H2 O2 ) is a promising alternative to the energetically intensive anthraquinone process. However, there remain challenges in designing 2 e- ORR catalysts that meet the application criteria. Here, we successfully adopt a microwave-assisted mechanochemical-thermal approach to synthesize hexagonal phase SnO2 (h-SnO2 ) nanoribbons with largely exposed edge structures. In 0.1 M Na2 SO4 electrolyte, the h-SnO2 catalysts achieve the excellent H2 O2 selectivity of 99.99 %. Moreover, when employed as the catalyst in flow cell devices, they exhibit a high yield of 3885.26 mmol g-1 h-1 . The enhanced catalytic performance is attributed to the special crystal structure and morphology, resulting in abundantly exposed edge active sites to convert O2 to H2 O2 , which is confirmed by density functional theory calculations.

RESUMEN

HYPOTHESIS: Electrochemical manufacture of H2O2 through the two-electron oxygen reduction reaction (2e- ORR), providing prospects of the distributed production of H2O2 in remote regions, is considered a promising alternative to the energy-intensive anthraquinone oxidation process. EXPERIMENTS: In this study, one glucose-derived oxygen-enriched porous carbon material (labeled as HGC500) is developed through a porogen-free strategy integrating structural and active site modification. FINDINGS: The superhydrophilic surface and porous structure together promote the mass transfer of reactants and accessibility of active sites in the aqueous reaction, while the abundant CO species (e.g., aldehyde groups) are taken for the main active site to facilitate the 2e- ORR catalytic process. Benefiting from the above merits, the obtained HGC500 possesses superior performance with a selectivity of 92 % and mass activity of 43.6 A gcat-1 at 0.65 V (vs. RHE). Besides, the HGC500 can operate steadily for 12 h with the accumulation of H2O2 reaching up to 4090±71 ppm and a Faradic efficiency of 95 %. The H2O2 generated from the electrocatalytic process in 3 h can degrade a variety of organic pollutants (10 ppm) in 4-20 min, displaying the potential in practical applications.

RESUMEN

Herein, a strategy of synergetic dual-metal-ion centers to boost transition-metal-based metal organic framework (MOF) alloy nanomaterials as active oxygen reduction reaction (ORR) electrocatalysts for efficient hydrogen peroxide (H2 O2 ) generation is proposed. Through a facile one-pot wet chemical method, a series of MOF alloys with unique Ni-M (M-Co, Cu, Zn) synergetic centers are synthesized, where the strong metallic ions 3d-3d synergy can effectively inhibit O2 cleavage on Ni sites toward a favorable two-electron ORR pathway. Impressively, the well-designed NiZn MOF alloy catalysts show an excellent H2 O2 selectivity up to 90% during ORR, evidently outperforming that of NiCo MOF (45%), and NiCu MOF (55%). Moreover, it sustains efficient activity and robust stability under a continuous longterm ORR operation. The correlative in situ synchrotron radiation X-ray adsorption fine structure and Fourier transform infrared spectroscopy analyses reveal at the atomic level that, the higher Ni oxidation states species, regulated via adjacent Zn2+ ions, are favorable for optimizing the adsorption energetics of key *OOH intermediates toward fast two electron ORR kinetics.

RESUMEN

Electrocatalytic oxygen reduction reaction (ORR) provides an attractive alternative to anthraquinone process for H2O2 synthesis. Rational design of earth-abundant electrocatalysts for H2O2 synthesis via a two-electron ORR process in acids is attractive but still very challenging. In this work, we report that nitrogen-doped carbon nanotubes as a multi-functional support for CoSe2 nanoparticles not only keep CoSe2 nanoparticles well dispersed but alter the crystal structure, which in turn improves the overall catalytic behaviors and thereby renders high O2-to-H2O2 conversion efficiency. In 0.1 M HClO4, such CoSe2@NCNTs hybrid delivers a high H2O2 selectivity of 93.2% and a large H2O2 yield rate of 172 ppm·h-1 with excellent durability up to 24 h. Moreover, CoSe2@NCNTs performs effectively for organic dye degradation via electro-Fenton process. Electronic Supplementary Material: Supplementary material (SEM images, EDX mapping images, XPS spectrum, XRD patterns, RRDE voltammogram, Tafel plots, cyclic voltammograms, UV-Vis spectra, and Tables S1) is available in the online version of this article at 10.1007/s12274-021-3474-0.

RESUMEN

Ambient electrochemical oxygen reduction into valuable hydrogen peroxide (H2O2) via a selective two-electron (2e-) pathway is regarded as a sustainable alternative to the industrial anthraquinone process, but it requires advanced electrocatalysts with high activity and selectivity. In this study, we report that Mn-doped TiO2 behaves as an efficient electrocatalyst toward highly selective H2O2 synthesis. This catalyst exhibits markedly enhanced 2e- oxygen reduction reaction performance with a low onset potential of 0.78 V and a high H2O2 selectivity of 92.7%, much superior to the pristine TiO2 (0.64 V, 62.2%). Additionally, it demonstrates a much improved H2O2 yield of up to 205 ppm h-1 with good stability during bulk electrolysis in an H-cell device. The significantly boosted catalytic performance is ascribed to the lattice distortion of Mn-doped TiO2 with a large amount of oxygen vacancies and Ti3+. Density functional theory calculations reveal that Mn dopant improves the electrical conductivity and reduces ΔG*OOH of pristine TiO2, thus giving rise to a highly efficient H2O2 production process.

RESUMEN

Hydrogen peroxide (H2 O2 ) is an environment-friendly and efficient oxidant with a wide range of applications in different industries. Recently, the production of hydrogen peroxide through direct electrosynthesis has attracted widespread research attention, and has emerged as the most promising method to replace the traditional energy-intensive multi-step anthraquinone process. In ongoing efforts to achieve highly efficient large-scale electrosynthesis of H2 O2 , carbon-based materials have been developed as 2e- oxygen reduction reaction catalysts, with the benefits of low cost, abundant availability, and optimal performance. This review comprehensively introduces the strategies for optimizing carbon-based materials toward H2 O2 production, and the latest advances in carbon-based hybrid catalysts. The active sites of the carbon-based materials and the influence of coordination heteroatom doping on the selectivity of H2 O2 are extensively analyzed. In particular, the appropriate design of functional groups and understanding the effect of the electrolyte pH are expected to further improve the selective efficiency of producing H2 O2 via the oxygen reduction reaction. Methods for improving catalytic activity by interface engineering and reaction kinetics are summarized. Finally, the challenges carbon-based catalysts face before they can be employed for commercial-scale H2 O2 production are identified, and prospects for designing novel electrochemical reactors are proposed.

RESUMEN

Electrocatalytic two-electron (2e-) oxygen reduction reaction (ORR) has been regarded as an efficient strategy to achieve onsite H2O2 generation under ambient conditions. However, due to the sluggish kinetics and competitive reaction between 2e- and 4e- ORR, exploring more efficient ORR catalysts with dominant 2e- ORR selectivity is of significance. Herein, hollow N-doped carbon spheres (HNCS) with abundant micropores through a template-directed method are presented. Consequently, the selectivity of the HNCS reaches ∼91.9% at 0.7 V (vs RHE), and the output for H2O2 production is up to 618.5 mmol gcatalyst-1 h-1 in 0.1 M KOH solution. The enhanced performance of HNCS for H2O2 electrosynthesis could be attributed to the hollow structure and heteroatom/defect/pore incorporation. The strategy presented here could shed light on the design of efficient carbon-based materials for improved 2e- ORR.

RESUMEN

Shifting electrochemical oxygen reduction reaction (ORR) via two-electron pathway becomes increasingly crucial as an alternative/green method for hydrogen peroxide (H2 O2 ) generation. Here, the development of 2e- ORR catalysts in recent years is reviewed, in aspects of reaction mechanism exploration, types of high-performance catalysts, factors to influence catalytic performance, and potential applications of 2e- ORR. Based on the previous theoretical and experimental studies, the underlying 2e- ORR catalytic mechanism is firstly unveiled, in aspect of reaction pathway, thermodynamic free energy diagram, limiting potential, and volcano plots. Then, various types of efficient catalysts for producing H2 O2 via 2e- ORR pathway are summarized. Additionally, the catalytic active sites and factors to influence catalysts' performance, such as electronic structure, carbon defect, functional groups (O, N, B, S, F etc.), synergistic effect, and others (pH, pore structure, steric hindrance effect, etc.) are discussed. The H2 O2 electrogeneration via 2e- ORR also has various potential applications in wastewater treatment, disinfection, organics degradation, and energy storage. Finally, potential future directions and prospects in 2e- ORR catalysts for electrochemically producing H2 O2 are examined. These insights may help develop highly active/selective 2e- ORR catalysts and shape the potential application of this electrochemical H2 O2 producing method.

RESUMEN

Carbon black (CB) has a high conductivity and a large surface area, which are the basis of an excellent electrocatalyst. However, CB itself is usually less active or even inactive toward two-electron oxygen reduction reaction (2e- ORR) due to the absence of highly active functional groups with low oxygen content. To activate commercial CB for 2e- ORR, oxygen-containing functional groups were introduced onto the CB surface by a simple air calcination method. After the oxidation treatment at 600 °C (CB600), the oxygen content increased from the initial 1.17 ± 0.15 to 4.08 ± 0.60%, leading to a dramatic increase of the cathodic current from only -8.1 mA (CB) to -117.6 mA (CB600). The air cathode made of CB600 achieved the maximum H2O2 production of 517.7 ± 2.4 mg L-1 within 30 min, resulting in the removal of ∼91.1% rhodamine B in 2 min and an effective mineralization of ∼76.3% in an electro-Fenton reactor. This performance was much better than that obtained using the CB catalyst (65.3 ± 5.6 mg L-1 H2O2 production, and ∼20.3% mineralization). This excellent activity of CB600 toward 2e- ORR was greatly improved by the introduction of O═C-OH and C-O-C groups. The successful improvement of the 2e- ORR activity of CB using air calcination enables its practical application in electrochemical advanced oxidation processes.