Recent Advances in the Direct Synthesis of Hydrogen Peroxide Using Chemical Catalysis—A Review

Improved H2O2 Electrosynthesis on S-doped Co-N-C through Cooperation of Co-S and Thiophene S

Co-N-C based catalysts have emerged as a prospective alternative for H2O2 electrosynthesis via a selective 2e- oxygen reduction reaction (ORR). However, conventional Co-N-C with Co-N4 configurations usually exhibits low selectivity toward 2e- ORR for H2O2 production. In this study, the S-doped Co-N-C (Co-N-C@S) catalysts were designed and synthesized for enhancing the electrosynthesis of H2O2, and their S doping levels and species were tuned to investigate their relationship with the H2O2 yield. The results showed that the S doping greatly enhanced the activity and selectivity of Co-N-C@S for H2O2 production. The optimal Co-N-C@S(12) displayed a high H2O2 production rate of 395 mmol gcat-1 h-1, H2O2 selectivity of 76.06%, and Faraday efficiency of 91.66% at 0.2 V, which were obviously better than those of Co-N-C (H2O2 production rate of 44 mmol gcat-1 h-1, H2O2 selectivity of 26.63%, and Faraday efficiency of 17.37%). Moreover, the Co-N-C@S(12) based electron-Fenton system displayed effective rhodamine B (RhB) removal, significantly outperforming the Co-N-C-based system. Experimental results combined with density functional theory unveiled that the enhanced performance of Co-N-C@S(12) stemmed from the combined effect of Co-S and thiophene S, which jointly enhanced electron density of the Co center, reduced the desorption energy of the *OOH intermediate, and then promoted the production of H2O2.

Electrifying Carbon Capture by Developing Nanomaterials at the Interface of Molecular and Process Engineering

ConspectusCarbon capture is an indispensable step toward closing the anthropogenic carbon cycle. However, the large-scale implementation of conventional thermochemical carbon capture technologies is hindered by their low energy efficiency, limited sorbent stability, and complexity in infrastructure integration. A mechanistically different alternative, commonly known as electrochemically mediated carbon capture (EMCC), has garnered increasing research traction over the past few years and relies on electrochemical stimuli instead of thermal or pressure swings for the capture and release of carbon dioxide (CO2). Compared to conventional methods, EMCC can be operated under mild conditions driven by intermittent renewable energy sources and has a flexible design to meet the multiscale demands of carbon capture, offering a potentially sustainable, energy-efficient, and cost-effective solution to CO2 concentration from dilute mixtures or the ambient environment.Nanomaterials have played a crucial role in carbon capture research. For instance, nanoporous materials can provide increased free volumes, surface areas, and active sites for carbon capture through physical or chemical adsorption from the gaseous phase. In contrast, EMCC relies on chemical absorption via acid-base interactions using solubilized CO2 in electrolytes. Therefore, most EMCC sorbents and mediators explored so far have been developed as molecules rather than nanomaterials. In recent years, our team has been focusing on electrifying the carbon capture processes at the molecular, materials, and process levels. We seek to address the most pressing issues associated with EMCC, either in fixed-bed or flow systems, that prevent their practical use. These issues include parasitic reactions with molecular oxygen, insufficient electrode capacity utilization, sorbent crossover, etc. To address these problems, there is an urgent need to develop rationally designed nanomaterials at the interface of molecular electrochemistry and device engineering. This Account provides an overview of recent progress on developing new chemistries and engineering batch/continuous processes for EMCC. We discuss the limitations of current EMCC technology and emphasize why nanomaterials are critical for electrifying carbon capture. First, we introduce the design principles for EMCC sorbents based on redox-active organic CO2 carriers and discuss metrics for their performance evaluation. Second, we showcase how molecular design can tackle problems of sorbent solubility, oxygen stability, and electrolyte compatibility in EMCC. Third, we discuss the early results of nanomaterials as solid sorbents in fixed-bed systems, nonswelling membranes for flow systems, and high-surface-area gas-liquid contactors. Finally, building on the foundation we established through our prior work, we offer perspectives on future directions for nanomaterials to help address the challenges in EMCC.

N-Doped porous carbons obtained from chitosan and spent coffee as electrocatalysts with tuneable oxygen reduction reaction selectivity for H2O2 generation

Nitrogen-containing porous carbons prepared by the pyrolysis of adequate biopolymer-based precursors have shown potential in several electrochemical energy-related applications. However, it is still of crucial interest to find the optimal precursors and process conditions which would allow the preparation of carbons with adequate porous structure as well as suitable nitrogen content and distribution of functional groups. In the present work we suggested a straightforward approach to prepare N-doped porous carbons by direct pyrolysis under nitrogen of chitosan : coffee blends of different compositions and using KOH for simultaneous surface activation. The synthetized carbon materials were tested for the electrochemical oxygen reduction to hydrogen peroxide (H₂O₂). A higher fraction of chitosan in the precursor led to a decrease in meso- and nano-porosity of the formed porous carbons, while their activity towards H₂O₂ generation increased. The nitrogen species derived from chitosan seem to play a very important role. Out of the synthesized catalysts the one with the largest content of pyridinic nitrogen sites exhibited the highest faradaic efficiency. The faradaic efficiencies and current densities of the synthesized materials were comparable with the ones of other commercially available carbons obtained from less renewable precursors.

Reusable Cobalt-Catalyzed Selective Transfer Hydrogenation of Azoarenes and Nitroarenes

Herein, control transfer hydrogenation (TH) of azoarenes to hydrazo compounds is established employing easy-to-synthesize reusable cobalt catalyst using lower amounts of N₂H₄·H₂O under mild conditions. With this effective methodology, a library of symmetrical and unsymmetrical azoarene derivatives was successfully converted to their corresponding hydrazo derivatives. Further, this protocol was extended to the TH of nitroarenes to amines with good-to-excellent yields. Several kinetic studies along with Hammett studies were carried out to understand the plausible mechanism and the electronic effects in this transformation. This inexpensive catalyst can be recycled up to five times without considerable loss of catalytic activity.

Strategies for Sustainable Production of Hydrogen Peroxide via Oxygen Reduction Reaction: From Catalyst Design to Device Setup

An environmentally benign, sustainable, and cost-effective supply of H2O2 as a rapidly expanding consumption raw material is highly desired for chemical industries, medical treatment, and household disinfection. The electrocatalytic production route via electrochemical oxygen reduction reaction (ORR) offers a sustainable avenue for the on-site production of H2O2 from O2 and H2O. The most crucial and innovative part of such technology lies in the availability of suitable electrocatalysts that promote two-electron (2e-) ORR. In recent years, tremendous progress has been achieved in designing efficient, robust, and cost-effective catalyst materials, including noble metals and their alloys, metal-free carbon-based materials, single-atom catalysts, and molecular catalysts. Meanwhile, innovative cell designs have significantly advanced electrochemical applications at the industrial level. This review summarizes fundamental basics and recent advances in H2O2 production via 2e--ORR, including catalyst design, mechanistic explorations, theoretical computations, experimental evaluations, and electrochemical cell designs. Perspectives on addressing remaining challenges are also presented with an emphasis on the large-scale synthesis of H2O2 via the electrochemical route.

Photocatalytic Synthesis of Hydrogen Peroxide from Molecular Oxygen and Water

Hydrogen peroxide is a powerful and green oxidant that allows for the oxidation of a wide span of organic and inorganic substrates in liquid media under mild reaction conditions, and forms only molecular water and oxygen as end products. Hydrogen peroxide is therefore used in a wide range of applications, for which the well-documented and established anthraquinone autoxidation process is by far the dominating production method at the industrial scale. As this method is highly energy consuming and environmentally costly, the search for more sustainable synthesis methods is of high interest. To this end, the article reviews the basis and the recent development of the photocatalytic synthesis of hydrogen peroxide. Different oxygen reduction and water oxidation mechanisms are discussed, as well as several kinetic models, and the influence of the main key reaction parameters is itemized. A large range of photocatalytic materials is reviewed, with emphasis on titania-based photocatalysts and on high-prospect graphitic carbon nitride-based systems that take advantage of advanced bulk and surface synthetic approaches. Strategies for enhancing the performances of solar-driven photocatalysts are reported, and the search for new, alternative, photocatalytic materials is detailed. Finally, the promise of in situ photocatalytic synthesis of hydrogen peroxide for water treatment and organic synthesis is described, as well as its coupling with enzymes and the direct in situ synthesis of other technical peroxides.

Progress and prospective of heterogeneous catalysts for H2O2 production via anthraquinone process

This paper reviews the improvement in the field of catalytic hydrogenation of 2-ethylanthraquinone to 2-ethylanthrahydroquinone for the successful production of hydrogen peroxide. Hydrogen peroxide is being used in almost all industrial areas, particularly in the chemical industry and in environmental protection, as the most promising oxidant for cleaner and environmentally safer processes. A variety of hydrogenation catalysts have been introduced for hydrogenation of 2-ethylanthraquinone in the production of hydrogen peroxide via anthraquinone (AQ) process. The aim of the present study is to describe the catalysts used in the hydrogenation of 2-ethylanthraquinone and the reaction mechanism involved with different catalytic systems. The hydrogenation of 2-ethylanthraquinone using metals, alloy, bimetallic composite, and supported metal catalyst with the structural modifications has been incorporated for the production of hydrogen peroxide. The comprehensive comparison reveals that the supported metal catalysts required lesser catalyst amount, produced lower AQ decay, and provided higher catalyst activity and selectivity. Furthermore, the replacement of conventional catalysts by metal and metal alloy-supported catalyst rises as a hydrogenation trend, enhancing by several times the catalytic performance.

Silica Bifunctional Supports for the Direct Synthesis of H2O2: Optimization of Br/Acid Sites and Pd/Br Ratio

We have studied the direct synthesis of hydrogen peroxide using a catalytic system consisting of palladium supported on silica bifunctionalized with sulfonic acid groups and bromide in the absence of acid and halide promoters in solution. Catalysts with several bromide substituents were employed in the catalyst synthesis. The prepared samples were characterized by TXRF, XPS, and hydrogen peroxide decomposition. Catalysts characterization indicated the presence of only palladium (II) species in all of the samples, with similar values for surface and bulk of Pd/Br atomic ratio. The catalysts were tested via direct synthesis, and all samples were able to produce hydrogen peroxide at 313 K and 5.0 MPa. The hydrogen peroxide yield and selectivity changed with the Pd/Br ratio. A decrease in the Pd/Br ratio increases the final hydrogen peroxide concentration, and the selectivity for H2O2 reaches a maximum at a Pd/Br ratio around 0.16 and then decreases. However, the maximum hydrogen peroxide concentration and selectivity occur at slightly different Pd/Br ratios, i.e., resp. 0.4 vs. 0.16.

Sustainable Approach for Peroxygenase-Catalyzed Oxidation Reactions Using Hydrogen Peroxide Generated from Spent Coffee Grounds and Tea Leaf Residues

Peroxygenases are promising catalysts for use in the oxidation of chemicals as they catalyze the direct oxidation of a variety of compounds under ambient conditions using hydrogen peroxide (H₂O₂) as an oxidant. Although the use of peroxygenases provides a simple method for oxidation of chemicals, the anthraquinone process currently used to produce H₂O₂ requires significant energy input and generates considerable waste, which negatively affects process sustainability and production costs. Thus, generating H₂O₂ for peroxygenases on site using an environmentally benign method would be advantageous. Here, we utilized spent coffee grounds (SCGs) and tea leaf residues (TLRs) for the production of H₂O₂. These waste biomass products reacted with molecular oxygen and effectively generated H₂O₂ in sodium phosphate buffer. The resulting H₂O₂ was utilized by the bacterial P450 peroxygenase, CYP152A1. Both SCG-derived and TLR-derived H₂O₂ promoted the CYP152A1-catalyzed oxidation of 4-methoxy-1-naphthol to Russig's blue as a model reaction. In addition, when CYP152A1 was incubated with styrene, the SCG and TLR solutions enabled the synthesis of styrene oxide and phenylacetaldehyde. This new approach using waste biomass provides a simple, cost-effective, and sustainable oxidation method that should be readily applicable to other peroxygenases for the synthesis of a variety of valuable chemicals.

Effects of g-C3N4 Heterogenization into Intrinsically Microporous Polymers on the Photocatalytic Generation of Hydrogen Peroxide

Graphitic carbon nitride (g-C₃N₄) is known to photogenerate hydrogen peroxide in the presence of hole quenchers in aqueous environments. Here, the g-C₃N₄ photocatalyst is embedded into a host polymer of intrinsic microporosity (PIM-1) to provide recoverable heterogenized photocatalysts without loss of activity. Different types of g-C₃N₄ (including Pt@g-C₃N₄, Pd@g-C₃N₄, and Au@g-C₃N₄) and different quenchers are investigated. Exploratory experiments yield data that suggest binding of the quencher either (i) directly by adsorption onto the g-C₃N₄ (as shown for α-glucose) or (ii) indirectly by absorption into the microporous polymer host environment (as shown for Triton X-100) enhances the overall photochemical H₂O₂ production process. The amphiphilic molecule Triton X-100 is shown to interact only weakly with g-C₃N₄ but strongly with PIM-1, resulting in accumulation and enhanced H₂O₂ production due to the microporous polymer host.

Heterogeneous Trimetallic Nanoparticles as Catalysts

The development and application of trimetallic nanoparticles continues to accelerate rapidly as a result of advances in materials design, synthetic control, and reaction characterization. Following the technological successes of multicomponent materials in automotive exhausts and photovoltaics, synergistic effects are now accessible through the careful preparation of multielement particles, presenting exciting opportunities in the field of catalysis. In this review, we explore the methods currently used in the design, synthesis, analysis, and application of trimetallic nanoparticles across both the experimental and computational realms and provide a critical perspective on the emergent field of trimetallic nanocatalysts. Trimetallic nanoparticles are typically supported on high-surface-area metal oxides for catalytic applications, synthesized via preparative conditions that are comparable to those applied for mono- and bimetallic nanoparticles. However, controlled elemental segregation and subsequent characterization remain challenging because of the heterogeneous nature of the systems. The multielement composition exhibits beneficial synergy for important oxidation, dehydrogenation, and hydrogenation reactions; in some cases, this is realized through higher selectivity, while activity improvements are also observed. However, challenges related to identifying and harnessing influential characteristics for maximum productivity remain. Computation provides support for the experimental endeavors, for example in electrocatalysis, and a clear need is identified for the marriage of simulation, with respect to both combinatorial element screening and optimal reaction design, to experiment in order to maximize productivity from this nascent field. Clear challenges remain with respect to identifying, making, and applying trimetallic catalysts efficiently, but the foundations are now visible, and the outlook is strong for this exciting chemical field.

Enhancing the catalytic performance of PdAu catalysts by W-induced strong interaction for the direct synthesis of H2O2

W-Induced strong interaction with PdAu is the key to the enhanced catalytic performance for the direct synthesis of H2O2, with WO3 species partially encapsulating the PdAu particles.

Catalytic CO Oxidation and H2O2 Direct Synthesis over Pd and Pt-Impregnated Titania Nanotubes

Titania nanotubes (TNTs) impregnated with Pd and Pt nanoparticles are evaluated as heterogeneous catalysts in different conditions in two reactions: catalytic CO oxidation (gas phase, up to 500 °C) and H2O2 direct synthesis (liquid phase, 30 °C). The TNTs are obtained via oxidation of titanium metal and the intermediate layer-type sodium titanate Na2Ti3O7. Thereafter, the titanate layers are exfoliated and show self-rolling to TNTs, which, finally, are impregnated with Pd or Pt nanoparticles at room temperature by using Pd(ac)2 and Pt(ac)2. The resulting crystalline Pd/TNTs and Pt/TNTs are realized with different lengths (long TNTs: 2.0–2.5 µm, short TNTs: 0.23–0.27 µm) and a specific surface area up to 390 m2/g. The deposited Pd and Pt particles are 2–5 nm in diameter. The TNT-derived catalysts show good thermal (up to 500 °C) and chemical stability (in liquid-phase and gas-phase reactions). The catalytic evaluation results in a low CO oxidation light-out temperature of 150 °C for Pt/TNTs (1 wt-%) and promising H2O2 generation with a productivity of 3240 molH2O2 kgPd−1 h−1 (Pd/TNTs, 5 wt-%, 30 °C). Despite their smaller surface area, long TNTs outperform short TNTs with regard to both CO oxidation and H2O2 formation.

Atomistic Insights into H2O2 Direct Synthesis of Ni-Pt Nanoparticle Catalysts under Water Solvents by Reactive Molecular Dynamics Simulations

In computational catalysis, density-functional theory (DFT) calculations are usually utilized, although they suffer from high computational costs. Thus, it would be challenging to explicitly predict the catalytic properties of nanoparticles (NPs) at the nanoscale under solvents. Using molecular dynamics (MD) simulations with a reactive force field (ReaxFF), we investigated the catalytic performance of Ni-Pt NPs for the direct synthesis of hydrogen peroxide (H₂O₂), in which water solvents were explicitly considered along with the effects of the sizes (1.5, 2.0, 3.0, and 3.5 nm) and compositions (Ni₉₀Pt₁₀, Ni₈₀Pt₂₀, and Ni₅₀Pt₅₀) of the NPs. Among the Ni-Pt NPs, 3.0 nm NPs show the highest activity and selectivity for the direct synthesis of H₂O₂, revealing that the catalytic performance is not well correlated with the surface areas of NPs. The superior catalytic performance results from the high H₂ dissociation and low O₂ dissociation properties, which are correlated with the numbers of NiNiPt-fcc and NiNi-bridge sites on the surface of Ni-Pt NPs, respectively. The ReaxFF-MD simulations propose the optimum composition (Ni₈₀Pt₂₀) of 3.0 nm Ni-Pt NPs, which is also explained by the numbers of NiNiPt-fcc and NiNi-bridge sites. Furthermore, from the ReaxFF-MD simulations, the direct synthesis of H₂O₂ for the Ni-Pt NPs can be achieved not only with the Langmuir-Hinshelwood mechanism, which has been conventionally considered, but also with the water-induced mechanism, which is unlikely to occur on pure Pd and Pd-based alloy catalysts; these results are supported by DFT calculations. These results reveal that the ReaxFF-MD method provides significant information for predicting the catalytic properties of NPs, which could be difficult to provide with DFT calculations; thus, it can be a useful framework for the design of nanocatalysts through complementation with a DFT method.

Stability and Influence of Storage Conditions on Nanofibrous Film Containing Tooth Whitening Agent

Carbamide peroxide (CP), a tooth whitening agent, is chemically unstable. The present study explores stability enhancement of CP by loading in a nanofibrous film (CP-F) composed of polyvinyl alcohol/polyvinylpyrrolidone/silica mixture, using an electrospinning technique. Kept at a temperature range of 60–80 °C for 6 h, CP in CP-F showed significantly higher stability than that in a polymer solution and in water, respectively. Degradation of CP in CP-F could be described by the first order kinetics with the predicted half-life by the Arrhenius equation of approximately 6.52 years. Physicochemical properties of CP-F after long-term storage for 12 months at different temperatures and relative humidity (RH) were investigated using scanning electron microscopy, X-ray diffractometry, differential scanning calorimetry, and Fourier transform infrared spectroscopy. It was found that high temperature and high humidity (45 °C/75% RH) could enhance water absorption and destruction of the nanofibrous structure of CP-F. Interestingly, kept at 25 °C/30% RH, the nanofibrous structure of CP-F was not damaged, and exhibited no water absorption. Moreover, the remaining CP, the mechanical properties, and the adhesive properties of CP-F were not significantly changed in this storage condition. It is concluded that the developed CP-F and a suitable storage condition can significantly improve CP stability.

NaCl-template-based synthesis of TiO2-Pd/Pt hollow nanospheres for H2O2 direct synthesis and CO oxidation

TiO2 hollow nanosphere (HNS) are prepared via NaCl templates in a one-pot approach. The NaCl templates are realized by solvent/anti-solvent strategies and coated with TiO2via controlled hydrolysis of Ti-alkoxides. The NaCl template can be easily removed by washing with water, and the TiO2 HNS are finally impregnated with Pd/Pt. Electron microscopy shows TiO2 HNS with an outer diameter of 140-180 nm, an inner cavity of 80-100 nm, and a wall thickness of 30-40 nm. The TiO2 HNS exhibit high surface area (up to 370 m2 g-1) and pore volume (up to 0.28 cm3 g-1) with well-distributed small Pd/Pt nanoparticles (Pt: 3-4 nm, Pd: 3-7 nm). H2O2 direct synthesis (room temperature, liquid phase) and CO oxidation (up to 300 °C, gas phase) are used to probe the catalytic properties and result in a good stability of the HNS structure as well as a promising performance with a H2O2 selectivity of 63% and a productivity of 3390 mol kgPd-1 h-1 (TiO2-Pd HNS, 5 wt%) as well as CO oxidation light-out temperatures of 150 °C (TiO2-Pt HNS, 0.7 wt%).

In situ H2O2 generation methods in the context of enzyme biocatalysis

Hydrogen peroxide is a versatile oxidant that has use in medical and biotechnology industries. Many enzymes require this oxidant as a reaction mediator in order to undergo their oxygenation chemistries. While there is a reliable method for generating hydrogen peroxide via an anthraquinone cycle, there are several advantages for generating hydrogen in situ. As highlighted in this review, this is particularly beneficial in the case of biocatalysts that require hydrogen peroxide as a reaction mediator because the exogenous addition of hydrogen peroxide can damage their reactive heme centers and render them inactive. In addition, generation of hydrogen peroxide in situ does not dilute the reaction mixture and cause solution parameters to change. The environment would also benefit from a hydrogen peroxide synthesis cycle that does not rely on nonrenewable chemicals obtained from fossil fuels. Generation of hydrogen peroxide in situ for biocatalysis using enzymes, bioelectrocatalyis, photocatalysis, and cold temperature plasmas are addressed. Particular emphasis is given to reaction processes that support high total turnover numbers (TTNs) of the hydrogen peroxide-requiring enzymes. Discussion of innovations in the use of hydrogen peroxide-producing enzyme cascades for antimicrobial activity, wastewater effluent treatment, and biosensors are also included.

A review on recent developments in electrochemical hydrogen peroxide synthesis with a critical assessment of perspectives and strategies

Electrochemical hydrogen peroxide synthesis using two-electron oxygen electrochemistry is an intriguing alternative to currently dominating environmentally unfriendly and potentially hazardous anthraquinone process and noble metals catalysed direct synthesis. Electrocatalytic two-electron oxygen reduction reaction (ORR) and water oxidation reaction (WOR) are the source of electrochemical hydrogen peroxide generation. Various electrocatalysts have been used for the same and were characterized using several electroanalytical, chemical, spectroscopic and chromatographic tools. Though there have been a few reviews summarizing the recent developments in this field, none of them have unified the approaches in catalysts' design, criticized the ambiguities and flaws in the methods of evaluation, and emphasized the role of electrolyte engineering. Hence, we dedicated this review to discuss the recent trends in the catalysts' design, performance optimization, evaluation perspectives and their appropriateness and opportunities with electrolyte engineering. In addition, particularized discussions on fundamental oxygen electrochemistry, additional methods for precise screening, and the role of solution chemistry of synthesized hydrogen peroxide are also presented. Thus, this review discloses the state-of-the-art in an unpresented view highlighting the challenges, opportunities, and alternative perspectives.

Recent advances in pincer-nickel catalyzed reactions

Organometallic catalysts have played a key role in accomplishing numerous synthetically valuable organic transformations that are either otherwise not possible or inefficient. The use of precious, sparse and toxic 4d and 5d metals are an apparent downside of several such catalytic systems despite their immense success over the last several decades. The use of complexes containing Earth-abundant, inexpensive and less hazardous 3d metals, such as nickel, as catalysts for organic transformations has been an emerging field in recent times. In particular, the versatile nature of the corresponding pincer-metal complexes, which offers great control of their reactivity via countless variations, has garnered great interest among organometallic chemists who are looking for greener and cheaper alternatives. In this context, the current review attempts to provide a glimpse of recent developments in the chemistry of pincer-nickel catalyzed reactions. Notably, there have been examples of pincer-nickel catalyzed reactions involving two electron changes via purely organometallic mechanisms that are strikingly similar to those observed with heavier Pd and Pt analogues. On the other hand, there have been distinct differences where the pincer-nickel complexes catalyze single-electron radical reactions. The applicability of pincer-nickel complexes in catalyzing cross-coupling reactions, oxidation reactions, (de)hydrogenation reactions, dehydrogenative coupling, hydrosilylation, hydroboration, C-H activation and carbon dioxide functionalization has been reviewed here from synthesis and mechanistic points of view. The flurry of global pincer-nickel related activities offer promising avenues in catalyzing synthetically valuable organic transformations.

Healthy Power: Reimagining Hospitals as Sustainable Energy Hubs

Human health is a key pillar of modern conceptions of sustainability. Humanity pays a considerable price for its dependence on fossil-fueled energy systems, which must be addressed for sustainable urban development. Public hospitals are focal points for communities and have an opportunity to lead the transition to renewable energy. We have reimagined the healthcare energy ecosystem with sustainable technologies to transform hospitals into networked clean energy hubs. In this concept design, hydrogen is used to couple energy with other on-site medical resource demands, and vanadium flow battery technology is used to engage the public with energy systems. This multi-generation system would reduce harmful emissions while providing reliable services, tackling the linked issues of human and environmental health.

Process Optimization for the Production of Ferric Sulfate Coagulant by the Oxidation of Ferrous sulfate with Hydrogen Peroxide

Motivated by the oxidative power of hydrogen peroxide and its environmentally attractive properties, the present study aimed to determine the optimum conditions for the production of ferric sulfate coagulant from ferrous sulfate The independent variables studied were the temperature (7.5–27.5 °C), amount of hydrogen peroxide (100–300 %) of the stoichiometric amount for the oxidation reaction, and dilution of the reaction medium using water (100–300 %) of the stoichiometric amount for the oxidation reaction. For the optimum conditions achieved, it was possible to obtain a conversion of 96.17 % of Fe+2to Fe+3, using a small hydrogen peroxide excess of 50 %, resulting in a product suitable for use as a coagulant in water treatment. It was found that an oxidation potential (Eh) greater than 0.7 volts corresponded to the conversion of Fe+2to Fe+3greater than 90 %, indicating Eh to be useful for reaction control in an industrial process.

Electrochemically derived functionalized graphene for bulk production of hydrogen peroxide

On-site peroxide generation via electrochemical reduction is gaining tremendous attention due to its importance in many fields, including water treatment technologies. Oxidized graphitic carbon-based materials have been recently proposed as an alternative to metal-based catalysts in the electrochemical oxygen reduction reaction (ORR), and in this work we unravel the role of C=O groups in graphene towards sustainable peroxide formation. We demonstrate a versatile single-step electrochemical exfoliation of graphite to graphene with a controllable degree of oxygen functionalities and thickness, leading to the formation of large quantities of functionalized graphene with tunable rate parameters, such as the rate constant and exchange current density. Higher oxygen-containing exfoliated graphene is known to undergo a two-electron reduction path in ORR having an efficiency of about 80 ± 2% even at high overpotential. Bulk production of H₂O₂ via electrolysis was also demonstrated at low potential (0.358 mV vs RHE), yielding ≈34 mg/L peroxide with highly functionalized (≈23 atom %) graphene and ≈16 g/L with low functionalized (≈13 atom %) graphene, which is on par with the peroxide production using state-of-the-art precious-metal-based catalysts. Hence this method opens a new scheme for the single-step large-scale production of functionalized carbon-based catalysts (yield ≈45% by weight) that have varying functionalities and can deliver peroxide via the electrochemical ORR process.

Synthesis of Pd-M@HCS(M = Co, Ni, Cu) Bimetallic Catalysts and Their Catalytic Performance for Direct Synthesis of H2O2

Hydrogen peroxide (H2O2), as a clean and green oxidant, is widely used in many fields. The direct synthesis of H2O2 (DSHP) from H2 and O2 has attracted most research interest because it relates to a facile, environmentally friendly, and economic process. Yolk–shell Pd-M@HCS (hollow carbon sphere) (M = Co, Ni, Cu) nanocatalysts, in which the bimetal nanoparticle is the core and porous carbon works as the shell layer, are reported in this work. It was found that catalytic activities were enhanced because of the introduced M metals. Additionally, the different mass ratios of Pd to Co (mPd/mCo) were further investigated to improve the catalytic performance for the DSHP. When mPd/mCo was 4.4, the prepared Pd-Co@HCS-(4.4) catalyst, with an average Pd nanoparticle size of 7.30 nm, provided the highest H2O2 selectivity of 87% and H2O2 productivity of 1996 mmolgPd−1·h−1, which were increased by 24% and 253%, respectively, compared to Pd@HCS.

A zinc-quinone battery for paired hydrogen peroxide electrosynthesis

Hydrogen peroxide is a commodity chemical with immense applications as an environmentally benign disinfectant for water remediation, a green oxidant for synthetic chemistry and pulp bleaching, an energy carrier molecule and a rocket propellant. It is typically synthesized by indirect batch anthraquinone process, where sequential hydrogenation and oxidation of anthraquinone molecules generates H₂O₂. This highly energy demanding catalytic sequence necessitates the advent of new reaction pathways with lower energy expenditure. Here we demonstrate a Zn-quinone battery for paired H₂O₂ electrosynthesis at the three phase boundary of its cathodic half-cell during electric power generation. The catalytic quinone half-cell of the Zn-quinone battery, mediates proton coupled electron transfer with molecular oxygen during its chemical regeneration thereby pairing peroxide electrosynthesis with electricity generation. Hydrogen peroxide synthesizing Zn-quinone battery (HPSB) demonstrated a peak power density of ~90 mW/cm² at a peak current density of ~145 mA/cm² while synthesizing ~230 mM of H₂O₂. HPSB offers immense opportunities as it distinctly couples electric power generation with peroxide electrosynthesis which in-turn transforms energy conversion in batteries truly multifunctional.

Enhancing the selectivity of Pd/C catalysts for the direct synthesis of H2O2 by HNO3 pretreatment

The acid functional groups of activated carbon improve the H₂O₂ selectivity.

Enhanced Photooxidation of Hydroquinone by Acetylacetone, a Novel Photosensitizer and Electron Shuttle

Quinones are important electron shuttles as well as micropollutants in the nature. Acetylacetone (AA) is a newly recognized electron shuttle in aqueous media exposed to UV irradiation. Herein, we studied the interactions between AA and hydroquinone (QH₂) under steady-state and transient photochemical conditions to clarify the possible reactions and consequences if QH₂ and AA coexist in a solution. Steady-state experimental results demonstrate that the interactions between AA and QH₂ were strongly affected by dissolved oxygen. In O₂-rich solutions, the phototransformation of QH₂ was AA-independent. Both QH₂ and AA utilize O₂ as the electron acceptor, but in O₂-insufficient solutions, AA became an important electron acceptor for the oxidation of QH₂. In all cases, the coexistence of AA increased the phototransformation of QH₂, whereas the decomposition of AA in O₂-saturated and oversaturated solutions was inhibited by the presence of QH₂. The underlying mechanisms were investigated by a combination of laser flash photolysis (LFP) and reduction potential analysis. The LFP results show that the excited AA serves as a better electron shuttle than QH₂. As a consequence, AA might regulate the redox cycling of quinones, leading to significant effects on many processes, ranging from photosynthesis and respiration to photodegradation.

A Comparative Study of the Catalytic Behaviour of Alkoxy-1,3,5-Triazapentadiene Copper(II) Complexes in Cyclohexane Oxidation

The mononuclear copper complexes [Cu{NH=C(OR)NC(OR)=NH}2] with alkoxy-1,3,5-triazapentadiene ligands that have different substituents (R = Me (1), Et (2), nPr (3), iPr (4), CH2CH2OCH3 (5)) were prepared, characterized (including the single crystal X-ray analysis of 3) and studied as catalysts in the mild oxidation of alkanes with H2O2 as an oxidant, pyridine as a promoting agent and cyclohexane as a main model substrate. The complex 4 showed the highest activity with a yield of products up to 18.5% and turnover frequency (TOF) up to 41 h−1. Cyclohexyl hydroperoxide was the main reaction product in all cases. Selectivity parameters in the oxidation of substituted cyclohexanes and adamantane disclosed a dominant free radical reaction mechanism with hydroxyl radicals as C–H-attacking species. The main overoxidation product was 6-hydroxyhexanoic acid, suggesting the presence of a secondary reaction mechanism of a different type. All complexes undergo gradual alteration of their structures in acetonitrile solutions to produce catalytically-active intermediates, as evidenced by UV/Vis spectroscopy and kinetic studies. Complex 4, having tertiary C–H bonds in its iPr substituents, showed the fastest alteration rate, which can be significantly suppressed by using the CD3CN solvent instead of CH3CN one. The observed process was associated to an autocatalytic oxidation of the alkoxy-1,3,5-triazapentadiene ligand. The deuterated complex 4-d32 was prepared and showed higher stability under the same conditions. The complexes 1 and 4 showed different reactivity in the formation of H218O from 18O2 in acetonitrile solutions.