Effects of porous structure and oxygen functionalities on electrochemical synthesis of hydrogen peroxide on ordered mesoporous carbon

Enhanced oxygen diffusion and catalytic performance of self-breathing CB/CNT cathodes for high-efficiency H2O2 production (in dual-chamber reactors)

A novel self-breathing gas diffusion electrode was developed by loading carbon nanotubes (CNTs) and carbon black (CB) onto the surface of graphite felt through vacuum filtration. This electrode features a well-structured mesoporous network and a stable three-phase interface, which enable efficient oxygen mass transfer and enhance the self-breathing capability. The incorporation of carbon nanotubes and carbon black significantly boosts the electrode's catalytic performance. In a dual-chamber reactor operating at a current density of 12 mA/cm2 and an initial pH of 3, the system achieved an H2O2 concentration of 4691 mg/L within 1 h, with an energy consumption of 6.58 kWh/kg H2O2 substantially outperforming conventional gas diffusion electrodes. The dynamic pH regulation in the dual-chamber system optimizes the 2e- ORR pathway, leading to corresponding changes in proton transfer pathways and adsorbed species within the Helmholtz plane. Additionally, the presence of reactive hydrogen (H∗) enhances the chemisorption of O2 and facilitates its hydrogenation to form the ∗OOH intermediate. The electrode exhibited excellent stability, maintaining H2O2 yields above 4000 mg/L over 5 cycles and nearly complete degradation of the simulated contaminants within 30 min in an electro-Fenton system application. These results highlight the electrode's potential for efficient H2O2 synthesis and environmental remediation.

Innovative engineering strategies and mechanistic insights for enhanced carbon-based electrocatalysts in sustainable H2O2 production

Hydrogen peroxide (H2O2) plays a crucial role in various industrial sectors and everyday applications. Given the energy-intensive nature of the current anthraquinone process for its production, the quest for cost-effective, efficient, and stable catalysts for H2O2 synthesis is paramount. A promising sustainable approach lies in small-scale, decentralized electrochemical methods. Carbon nanomaterials have emerged as standout candidates, offering low costs, high surface areas, excellent conductivity, and adjustable electronic properties. This review presents a thorough examination of recent strides in engineering strategies of carbon-based nanomaterials for enhanced electrochemical H2O2 generation. It delves into tailored microstructures (e.g., 1D, 2D, porous architectures), defect/surface engineering (e.g., edge sites, heteroatom doping, surface modification), and heterostructure assembly (e.g., semiconductor-carbon composites, single-atom, dual-single-atom catalysts). Moreover, the review explores structure-performance interplays in these carbon electrocatalysts, drawing from advanced experimental analyses and theoretical models to unveil the mechanisms governing selective electrocatalytic H2O2 synthesis. Lastly, this review identifies challenges and charts future research avenues to propel carbon electrocatalysts towards greener and more effective H2O2 production methods.

Employing a Zn-air/Photo-Electrochemical Cell for In Situ Generation of H2O2 for Onsite Control of Pollutants

Industrial production of hydrogen peroxide (H2O2) is energy-intensive and generates unwanted byproducts. Herein, an alternative production strategies of H2O2 are demonstrated in a Zn-air and a photoelectrochemical cell. Employing an optimally produced reduced graphene oxide (rGO) electrocatalyst@air-cathode, an impressive power density of 320 Wmgeo -2 (geo = geometric area) is achieved along with a high H2O2 production rate of 3.17 mol mgeo -2h-1 (operating potential = 0.8 V). Systematic investigations reveal the critical role of specific functional groups (viz. C─O─C, chemisorbed O2, C≐C) to be responsible for enhancing the yield of H2O2. The in situ generated superoxide (O2˙) and hydroxyl radicals (˙OH) act as oxidants to efficiently degrade onsite, a model textile dye pollutant (viz. rhodamine B) inside the Zn-air cell. Using the identical rGO as the photoelectrode in an H-type cell, the H2O2 production is remarkably enhanced under visible light illumination. Simultaneously, the onsite pollutant degradation occurs five times faster than the Zn-air cell (at the same operating potential = 0.8 V). This work opens a new paradigm for electrosynthesis, wherein an underlying redox can be utilized to synthesize industrial chemicals for onsite control of environmental pollution sustainably.

Mesoporous Boron-Doped Carbon with Curved B4C Active Sites for Highly Efficient H2O2 Electrosynthesis in Neutral Media and Air-Supplied Environments

Hydrogen peroxide (H2O2) electrosynthesis via the 2e- oxygen reduction reaction (ORR) is considered as a cost-effective and safe alternative to the energy-intensive anthraquinone process. However, in more practical environments, namely, the use of neutral media and air-fed cathode environments, slow ORR kinetics and insufficient oxygen supply pose significant challenges to efficient H2O2 production at high current densities. In this work, mesoporous B-doped carbons with novel curved B4C active sites, synthesized via a carbon dioxide (CO2) reduction using a pore-former agent, to simultaneously achieve excellent 2e- ORR activity and improved mass transfer properties are introduced. Through a combination of experimental analysis and theoretical calculations, it is confirmed that the curved B4C configuration, formed by mesopores in the carbon, demonstrates superior selectivity and activity for 2e- ORR due to its weaker interaction with *OOH intermediates compared to planar B4C in neutral media. Moreover, the mesopores facilitate oxygen supply and suppress the hydrogen evolution reaction, achieving a Faradaic efficiency of 86.2% at 150 mA cm-2 under air-supplied conditions, along with an impressive O2 utilization efficiency of 93.6%. This approach will provide a route to catalyst design for efficient H2O2 electrosynthesis in a practical environment.

Multifunctional Strategies of Advanced Electrocatalysts for Efficient Urea Synthesis

The electrochemical reduction of nitrogenous species (such as N2, NO, NO2 -, and NO3 -) for urea synthesis under ambient conditions has been extensively studied due to their potential to realize carbon/nitrogen neutrality and mitigate environmental pollution, as well as provide a means to store renewable electricity generated from intermittent sources such as wind and solar power. However, the sluggish reaction kinetics and the scarcity of active sites on electrocatalysts have significantly hindered the advancement of their practical applications. Multifunctional engineering of electrocatalysts has been rationally designed and investigated to adjust their electronic structures, increase the density of active sites, and optimize the binding energies to enhance electrocatalytic performance. Here, surface engineering, defect engineering, doping engineering, and heterostructure engineering strategies for efficient nitrogen electro-reduction are comprehensively summarized. The role of each element in engineered electrocatalysts is elucidated at the atomic level, revealing the intrinsic active site, and understanding the relationship between atomic structure and catalytic performance. This review highlights the state-of-the-art progress of electrocatalytic reactions of waste nitrogenous species into urea. Moreover, this review outlines the challenges and opportunities for urea synthesis and aims to facilitate further research into the development of advanced electrocatalysts for a sustainable future.

Recent Advances on Carbon-Based Metal-Free Electrocatalysts for Energy and Chemical Conversions

Over the last decade, carbon-based metal-free electrocatalysts (C-MFECs) have become important in electrocatalysis. This field is started thanks to the initial discovery that nitrogen atom doped carbon can function as a metal-free electrode in alkaline fuel cells. A wide variety of metal-free carbon nanomaterials, including 0D carbon dots, 1D carbon nanotubes, 2D graphene, and 3D porous carbons, has demonstrated high electrocatalytic performance across a variety of applications. These include clean energy generation and storage, green chemistry, and environmental remediation. The wide applicability of C-MFECs is facilitated by effective synthetic approaches, e.g., heteroatom doping, and physical/chemical modification. These methods enable the creation of catalysts with electrocatalytic properties useful for sustainable energy transformation and storage (e.g., fuel cells, Zn-air batteries, Li-O2 batteries, dye-sensitized solar cells), green chemical production (e.g., H2O2, NH3, and urea), and environmental remediation (e.g., wastewater treatment, and CO2 conversion). Furthermore, significant advances in the theoretical study of C-MFECs via advanced computational modeling and machine learning techniques have been achieved, revealing the charge transfer mechanism for rational design and development of highly efficient catalysts. This review offers a timely overview of recent progress in the development of C-MFECs, addressing material syntheses, theoretical advances, potential applications, challenges and future directions.