High-rate electrochemical H_(2)O_(2) production over multimetallic atom catalysts under acidic–neutral conditions

Hydrogen peroxide(H_(2)O_(2))production by the electrochemical 2-electron oxygen reduction reaction(2e−ORR)is a promising alternative to the energy-intensive anthraquinone process,and single-atom electrocatalysts show the unique capability of high selectivity toward 2e−ORR against the 4e−one.The extremely low surface density of the single-atom sites and the inflexibility in manipulating their geometric/electronic configurations,however,compromise the H_(2)O_(2) yield and impede further performance enhancement.Herein,we construct a family of multiatom catalysts(MACs),on which two or three single atoms are closely coordinated to form high-density active sites that are versatile in their atomic configurations for optimal adsorption of essential*OOH species.Among them,the Cox–Ni MAC presents excellent electrocatalytic performance for 2e−ORR,in terms of its exceptionally high H_(2)O_(2) yield in acidic electrolytes(28.96 mol L^(−1) gcat.^(−1) h^(−1))and high selectivity under acidic to neutral conditions in a wide potential region(>80%,0–0.7 V).Operando X-ray absorption and density functional theory analyses jointly unveil its unique trimetallic Co2NiN8 configuration,which efficiently induces an appropriate Ni–d orbital filling and modulates the*OOH adsorption,together boosting the electrocatalytic 2e−ORR capability.This work thus provides a new MAC strategy for tuning the geometric/electronic structure of active sites for 2e−ORR and other potential electrochemical processes.

Unveiling the chemistry behind the electrolytic production of hydrogen peroxide by oxygenated carbon

Oxygenated carbon materials exhibit outstanding electrocatalytic performance in the production of hydrogen peroxide(H2O2)through a two-electron oxygen reduction reaction.The nature of the active functional group and underlying reaction mechanism,however,remain unclear.Here,a comprehensive workflow was established to identify the active sites from the numerous possible structures.The common hydroxyl group at the notched edge demonstrates a key role in the two-electron process.The local chemical environment weakens the binding of OOH intermediate to substrate while enhancing interaction with solution,thereby promoting the H_(2)O_(2)production.With increasing pH,the intramolecular hydrogen bond between OOH intermediate and hydroxyl decreases,facilitating OOH desorption.Furthermore,the rise in selectivity with increasing potential stems from the suppression of the four-electron process.The active site was further validated through experiments.Guided by theoretical understanding,optimal performance was achieved with high selectivity(>95%)and current density(2.06 mA/cm^(2))in experiment.

Marrying luminescent metal nanoclusters to C_(3)N_(4) for efficient photocatalytic hydrogen peroxide production

Photocatalytic oxygen(O_(2))reduction has been considered a promising method for hydrogen peroxide(H_(2)O_(2))production.However,the poor visible light harvesting and low-efficient separation and generation of charge carriers of conventional photocatalysts strongly limited their photocatalytic H_(2)O_(2) generation performance.Herein,we design a highly efficient photocatalyst in this work by marrying luminescent gold-silver nanoclusters(AuAg NCs)to polyethyleneimine(PEI)modified C_(3)N_(4)(C3N4-PEI).The key design in this work is the utilization of highly luminescent AuAg NCs as photosensitizers to promote the generation and separation of charge carriers of C_(3)N_(4)-PEI,thereby ultimately producing abundant e−for O_(2) reduction under visible light illumination(λ≥400 nm).As a result,the as-designed photocatalyst(C3N4-PEI-AuAg NCs)exhibits excellent photocatalytic activity with an H_(2)O_(2) production capability of 82μM in pure water,which is 3.5 times higher than pristine C_(3)N_(4)(23μM).This interesting design provides a paradigm in developing other high-efficient photocatalysts for visible-light-driven H_(2)O_(2) production.

Recent progress in production and usage of hydrogen peroxide

Hydrogen peroxide has attracted increasing interest as an environmentally benign and green oxidant that can also be used as a solar fuel in fuel cells.This review focuses on recent progress in production of hydrogen peroxide by solar-light-driven oxidation of water by dioxygen and its usage as a green oxidant and fuel.The photocatalytic production of hydrogen peroxide is made possible by combining the e^(-)and 4e-oxidation of water with the e^(-)reduction of dioxygen using solar energy.The catalytic control of the selectivity of the e^(-)vs.4e-oxidation of water is discussed together with the selectivity of the e^(-)vs.4e-reduction of dioxygen.The combination of the photocatalytic e^(-)oxidation of water and the e^(-)reduction of dioxygen provides the best efficiency because both processes afford hydrogen peroxide.The solar-light-driven hydrogen peroxide production by oxidation of water and by reduction of dioxygen is combined with the catalytic oxidation of substrates with hydrogen peroxides,in which dioxygen is used as the greenest oxidant.

Effect of calcination temperatures on photocatalytic H_(2)O_(2)-production activity of ZnO nanorods

Photocatalytic hydrogen peroxide(H_(2)O_(2))production from O_(2) and H2O is an ideal process for solar‐to‐chemical energy conversion.Herein,ZnO nanorods are prepared via a simple hydrothermal method for photocatalytic H_(2)O_(2) production.The ZnO nanorods exhibit varied performance with different calcination temperatures.Benefiting from calcination,the separation efficiency of photo‐induced carriers is significantly improved,leading to the superior photocatalytic activity for H_(2)O_(2) production.The H_(2)O_(2) produced by ZnO calcined at 300℃ is 285μmol L^(−1),which is over 5 times larger than that produced by untreated ZnO.This work provides an insight into photocatalytic H2O2 production mechanism by ZnO nanorods,and presents a promising strategy to H2O2 production.

An efficient strategy for photocatalytic hydrogen peroxide production over oxygen-enriched graphitic carbon nitride with sodium phosphate

Photocatalytic hydrogen peroxide(H_(2)O_(2))production is a promising strategy to replace the traditional production processes;however,the inefficient H_(2)O_(2) productivity limits its application.In this study,oxygen-rich g-C_(3)N_(4) with abundant nitrogen vacancies(OCN)was synthesized for photocatalytic H_(2)O_(2) production.X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy indicated that oxygen-containing functional groups(–COOH and C–O–C)were obtained.Electron paramagnetic resonance confirmed the successful introduction of nitrogen vacancies.OCN exhibited efficient photocatalytic H_(2)O_(2) production performance of 1965μmol L^(−1) h^(−1) in air under visible-light irradiation.The high H_(2)O_(2) production was attributed to the enhanced adsorption of oxygen,enlarged specific surface area,and promoted carrier separation.An increased H_(2)O_(2) production rate(5781μmol L^(−1) h^(−1))was achieved in a Na_(3)PO_(4) solution.The improved performance was attributed to the changed reactive oxygen species.Specifically,the adsorbed PO_(4)^(3−) on the surface of the OCN promoted the transfer of holes to the catalyst surface.•O_(2)−obtained by O_(2) reduction reacted with adjacent holes to generate 1O_(2),which could efficiently generate H_(2)O_(2) with isopropanol.Additionally,PO_(4)^(3−),as a stabilizer,inhibited the decomposition of H_(2)O_(2).

Molecular engineering towards dual surface local polarization sites on poly(heptazine imide)framework for boosting H_(2)O_(2) photo-production

The selective 2e^(−)ORR reaction on polymeric carbon nitride framework is one of the most promising approaches for solar-driven hydrogen peroxide production.Poly(heptazine imide)(PHI)as a class of K+-incorporated crystalline carbon nitride framework,is highly active for photocatalytic H_(2)O_(2)production.An upgrade on the H_(2)O_(2)photoproduction performance of PHI is realized and the mechanistic insights are revealed in this work.By photochemical reaction,the electron withdrawing groups of hydroxyl group and cyano group are grafted on the surface of PHI frameworks.The dual polarization sites on the sur-face contribute significantly to the enhancement of the exciton dissociation.The optimized PHI with dual polarization sites exhibits a remarkable photocatalytic H_(2)O_(2)production performance,which is 2times of the active pristine PHI.Most importantly,the photochemical reaction method is generally applicable to improve the exciton dissociation of a wide range of polymeric carbon nitride frameworks with vari-ous structure and compositions;and the thiourea-derived polymeric carbon nitride framework with dual surface polarization sites exhibits a remarkable photocatalytic performance with a high H_(2)O_(2)production rate of 40.5 mmol h^(−1)g^(−1).

Cationic surface polarization centers on ionic carbon nitride for efficient solar-driven H_(2)O_(2) production and pollutant abatement

Solar-driven H_(2)O_(2)production and emerging organic pollutants(EOPs)elimination are of great significance from the perspective of environmental sustainability.The efficiency of the photocatalytic reaction system is the key challenge to be addressed.In this work,the strategy of constructing surface ionic local polarization centers to enhance the exciton dissociation of the polymeric photocatalytic is demonstrated.Selected bipyridinium cation(TMAP)is complexed on a K^(+)-incorporated carbon nitride(CNK)framework,and the combination of local polarization centers both on the surface(bipyridinium cation)and bulk(K+cation)contributes to a superior photocatalytic H_(2)O_(2)production performance,affording a remarkable H_(2)O_(2)generation rate of 46.8μmol h^(-1)mg^(-1)and a high apparent quantum yield(AQY)value of 77.5%under irradiation of 405 nm photons.As substantiated experimentally by steady state/transient spectroscopy techniques,the surface local polarization centers increase the population of the long-lived trapped electrons,and thereby promote the interfacial charge transfer process for chemical conversion reaction.The strategy is potentially applicable to the design of a wide range of efficient solar-to-chemical conversion systems.

Fullerene-derived boron-doped defective nanocarbon for highly selective H_(2)O_(2) electrosynthesis

Electrochemical production of hydrogen peroxide(H_(2)O_(2))via the two-electron(2e-)pathway of oxygen reduction reaction(ORR)supplies an auspicious alternative to the current industrial anthraquinone process.Nonetheless,it still lacks efficient electrocatalysts to achieve high ORR activity together with 2e-selectivity simultaneously.Herein,a boron-doped defective nanocarbon(B-DC)electrocatalyst is synthesized by using fullerene frameworks as the precursor and boric oxide as the boron source.The obtained B-DC materials have a hierarchical porous structure,befitting boron dopants,and abundant topological pentagon defects,exhibiting a high ORR onset potential of 0.78 V and a dominated 2e-selectivity(over 95%).Remarkably,when B-DC electrocatalyst is employed in a real device,it achieves a high H_(2)O_(2) yield rate(247 mg·L^(-1)·h^(-1)),quantitative Faraday efficiency(~100%),and ultrafast organic pollutant degradation rate.The theoretical calculation reveals that the synergistic effect of topological pentagon defects and the incorporation of boron dopants promote the activation of the O_(2) molecule and facilitates the desorption of oxygen intermediate.This finding will be very helpful for the comprehension of the synergistic effect of topological defects and heteroatom dopants for boosting the electrocatalytic performance of nanocarbon toward H_(2)O_(2) production.

Surface Oxidation of Single-walled-carbon-nanotubes with Enhanced Oxygen Electroreduction Activity and Selectivity

Electrochemical oxygen reduction reaction(ORR) with 2-electron process is an alternative for decentralized H_(2)O_(2) production, but it remains high challenging to develop highly active and selective catalysts for this process. In this work, we present a selective and efficient nonprecious electrocatalyst, prepared through an easily scalable mild oxidation of single-walled carbon nanotubes(SWNTs) with different oxidative acids including sulfur acid, nitride acid and mixed sulfuric/nitric acids, respectively. The high-degree oxidized SWNTs treated by mixed acids exhibit the highest activity and selectivity of electroreduction of oxygen to synthesize H_(2)O_(2) at low overpotential in alkaline and neutral media. Spectroscopic characterizations suggested that the C–O is vital for catalyzing 2-electron ORR, providing an insightful understanding of defected carbon surface as the active catalytic sites for 2-electron ORR.

Enhancing photocatalytic hydrogen peroxide production of Tibased metal-organic frameworks:The leading role of facet engineering

Rational construction of the facet engineering over metal-organic frameworks is of significant interest for enhancing photocatalytic performance,yet the role of modulator except regulating facet is largely ignored.Herein,facet engineering of NH_(2)-MIL125(aMIL)was achieved through the facile one-pot method by controlling the concentration of acetic acid modulator.The probable domino effects induced with the detectable modulator were extensively investigated,evidencing the multi-position in one mode contained powder X-Ray diffraction(PXRD),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),and X-ray absorption spectroscopy(XAS),etc.Meanwhile,correlation among the{111}facets engineering,the degree of structural defects,and the performance of photocatalytic hydrogen peroxide(H_(2)O_(2))production was studied in detail,revealing that facet and defect engineering respectively play positive and relatively negative roles in the photocatalytic oxygen reduction reaction(ORR)with a volcano-type trend.aMIL-3 photocatalyst could deliver H_(2)O_(2) production rate of 925.8μmol·h^(−1)·g^(−1)(2.03-fold of aMIL)under visible-light irradiation and a quantum yield of 1.08%at 420 nm.

Aqueous Synthesis of Covalent Organic Frameworks as Photocatalysts for Hydrogen Peroxide Production

Covalent organic frameworks(COFs)are crystalline porous polymers with designable structures and properties.Their crystallization typically relies on trialand-error experimentation involving harsh conditions,including organic solvents,presenting significant obstacles for rational design and large-scale production.Herein,we present a liquid crystal-directed synthesis methodology and its implementation for up to gram-scale production of highly crystalline COFs in water and air.It is compatible with monomers of different structures,shape,size,length of side chains,and electron-donating,electron-accepting,and heterocyclic substitutions near reactive sites.Seventeen types of donor-acceptor two-dimensional COFs including four types of new ones and a three-dimensional COF with a yield of up to 94%were demonstrated,showing great generality of the method.The as-synthesized donor-acceptor COFs are organic semiconductors and contain macropores besides intrinsic mesopores which make them attractive catalysts.The production of H_(2)O_(2)under visible light in water was studied and the structure-property relationships were revealed.The production rate reached 4347μmol h^(−1)gcat^(−1),which is about 467%better than that of the benchmark photocatalyst g-C_(3)N_(4).This study will inspire the mild synthesis and scale-up of a wide spectrum of COFs and organic semiconductors as efficient catalysts,promote their structure-property investigation,and boost their applications.

The atomic interface effect of single atom catalysts for electrochemical hydrogen peroxide production

Producing hydrogen peroxide(H_(2)O_(2))through an electrochemical oxygen reduction reaction(ORR)is a safe,green strategy and a promising alternative to traditional energy-intensive anthraquinone processes.Air and renewable power could be utilized for onsite and decentralized H_(2)O_(2)production,demonstrating significant application potential.Currently,single atom catalysts(SACs)have demonstrated significant advantages in the catalytic production of H_(2)O_(2)in 2e−ORR.However,the selectivity of SACs in ORR once puzzled researchers.This article reviews the research on the development and achievements of H_(2)O_(2)production by SACs catalysis in recent years.Especially,the structure-performance relationship is a guide to designing new SACs.Combining advanced characterization techniques and theoretical calculation methods,researchers have a clearer and more thorough understanding of the impact of the atomic interface of SACs on ORR catalytic performance.The coordination moiety formed between the active metal center atom and the support seriously determines the selectivity of SACs,mainly manifested in the adsorption of*OOH intermediates.Particularly,the atomic interface of metal atoms together with O/N co-coordination exhibit high selectivity and mass activity,and heteroatoms or functional groups on carbon supports present synergistic effects to promote the production of H_(2)O_(2)in 2e−ORR.Fine and accurate regulation of the atomic interface of SACs directly affects the 2e−ORR performance of the catalysts.Therefore,it is important to deeply understand the atomic interface of SACs and contribute to the development of novel catalysts.

Efficient production of hydrogen peroxide in microbial reverse-electrodialysis cells coupled with thermolytic solutions

H_(2)O_(2) was produced at an appreciable rate in microbial reverse-electrodialysis cells(MRCs)coupled with thermolytic solutions,which can simultaneously capture waste heat as electrical energy.To determine the optimal cathode and membrane stack configurations for H_(2)O_(2) production,different catalysts,catalyst loadings and numbers of membrane cell pairs were tested.Carbon black(CB)outperformed activated carbon(AC)for H_(2)O_(2) production,although AC showed higher catalytic activity for oxygen reduction.The optimum CB loading was 10 mg/cm^(2) in terms of both the H_(2)O_(2) production rate and power production.The optimum number of cell pairs was determined to be three based on a tradeoff between H_(2)O_(2) production and capital costs.A H_(2)O_(2) production rate as high as 0.99±0.10 mmol/(L·h)was achieved with 10 mg/cm^(2) CB loading and 3 cell pairs,where the H_(2)O_(2) recovery efficiency was 52±2%and the maximum power density was 780±37 mW/m^(2).Increasing the number of cell pairs to five resulted in an increase in maximum power density(980±21 mW/m^(2))but showed limited effects on H_(2)O_(2) production.These results indicated that MRCs can be an efficient method for sustainable H_(2)O_(2) production.

Flower-like superstructure of boron carbon nitride nanosheets with adjustable band gaps for photocatalytic hydrogen peroxide production

The self-assembly of two-dimensional(2D)semiconductor nanosheets into three-dimensional(3D)ordered superstructures represents an ingenious way to avoid aggregation,expose massive available active sites and benefit the mass transfer,which maximizes the advantages of the 2D nanostructures in photo-catalysis.Herein,a flower-like superstructure of ternary semiconducting boron carbon nitride nanosheets(FS-BCNNSs)was synthesized through the morphology-preserved thermal transformation of a flower-like superstructure of boron-containing metal-organic framework nanosheets(FS-MOFNSs).Taking advantage of this functional superstructure,FS-BCNNSs was employed for the pioneering application in the field of photocatalytic hydrogen peroxide(H_(2)O_(2))production and exhibited excellent photocatalytic performance,yielding an impressive rate of 1415.9μmol g^(−1)h^(−1)for the production of H_(2)O_(2).The results of this work offer not just a promising catalyst for photocatalytic H_(2)O_(2)production but also a facile strategy to fabricate unique superstructures constructed from 2D nanosheets for catalysis,energy conversion,and other related fields.