N, O-coupling towards the selectively electrochemical production of H2O2

Advanced Nanocarbons Toward two-Electron Oxygen Electrode Reactions for H2O2 Production and Integrated Energy Conversion

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.

General Design Concept of High-Performance Single-Atom-Site Catalysts for H2O2 Electrosynthesis

Hydrogen peroxide (H2O2) as a green oxidizing agent is widely used in various fields. Electrosynthesis of H2O2 has gradually become a hotspot due to its convenient and environment-friendly features. Single-atom-site catalysts (SASCs) with uniform active sites are the ideal catalysts for the in-depth study of the reaction mechanism and structure-performance relationship. In this review, the outstanding achievements of SASCs in the electrosynthesis of H2O2 through 2e- oxygen reduction reaction (ORR) and 2e- water oxygen reaction (WOR) in recent years, are summarized. First, the elementary steps of the two pathways and the roles of key intermediates (*OOH and *OH) in the reactions are systematically discussed. Next, the influence of the size effect, electronic structure regulation, the support/interfacial effect, the optimization of coordination microenvironments, and the SASCs-derived catalysts applied in 2e- ORR are systematically analyzed. Besides, the developments of SASCs in 2e- WOR are also overviewed. Finally, the research progress of H2O2 electrosynthesis on SASCs is concluded, and an outlook on the rational design of SASCs is presented in conjunction with the design strategies and characterization techniques.

Highly-efficient natural gas desulfurization and simultaneous H2O2 synthesis based on the electrochemical coupling reaction strategy

Hydrogen sulfide (H2S) generated by natural gas exploitation is a dangerous and harmful gas that needs to be purified. Electrochemical Natural Gas Desulfurization offers a promising way for H2S purification and resource utilization in ambient conditions. However, poor energy efficiency and low resource value limit the prospective application in the industry. Herein, we propose a gas-liquid flow electrocatalysis system that couples H2S oxidation and O2 reduction processes to effectively recover sulfur and H2O2 with low energy consumption. Gas diffusion and mass transfer are accelerated by gas-liquid flow cells, which also significantly decrease the resistance. Besides, I-/I3- redox pairs promote selective H2S oxidation while inhibiting water decomposition, resulting in a 56% reduction in oxidation potential. Moreover, the surface proton concentration is elevated by employing a modified carbon gas diffusion electrode (GDE), which assists to maintains a high H2O2 faradic efficiency. The system is able to operate at a high current density of 102 mA/cm2 at an Ecell voltage of 3.5 V, yielding S and H2O2 at rates of 60 mg cm-2 h-1 and 50 mg cm-2 h-1 respectively. A techno-economic model forecasts the effects of system efficiency and energy prices on operational costs and illustrates potential routes to a plant-gate levelized application in the petrochemical industry.

Carbon Catalysts Empowering Sustainable Chemical Synthesis via Electrochemical CO2 Conversion and Two-Electron Oxygen Reduction Reaction

Carbon materials hold significant promise in electrocatalysis, particularly in electrochemical CO2 reduction reaction (eCO2 RR) and two-electron oxygen reduction reaction (2e- ORR). The pivotal factor in achieving exceptional overall catalytic performance in carbon catalysts is the strategic design of specific active sites and nanostructures. This work presents a comprehensive overview of recent developments in carbon electrocatalysts for eCO2 RR and 2e- ORR. The creation of active sites through single/dual heteroatom doping, functional group decoration, topological defect, and micro-nano structuring, along with their synergistic effects, is thoroughly examined. Elaboration on the catalytic mechanisms and structure-activity relationships of these active sites is provided. In addition to directly serving as electrocatalysts, this review explores the role of carbon matrix as a support in finely adjusting the reactivity of single-atom molecular catalysts. Finally, the work addresses the challenges and prospects associated with designing and fabricating carbon electrocatalysts, providing valuable insights into the future trajectory of this dynamic field.

Rapid, in situ synthesis of ultra-small silicon particles for boosted lithium storage capability through ultrafast Joule heating

High-capacity anodes, especially silicon, suffer from huge volume fluctuations and electrode material pulverization during lithiation/delithiation. An accessible solution to this issue is to construct nano-silicon anodes with optimized particle size and a conductive matrix. In this work, we introduce a novel strategy for the in situ, rapid synthesis of ultra-small silicon nanoparticles uniformly embedded within carbonized nanosheets (us-Si/C) through swift high-temperature thermal radiative heating of sizable silicon nanoparticles (SiNPs). The us-Si/C anode shows ample capability to accommodate volume fluctuations during the lithiation/delithiation processes. The as-prepared anode exhibits a specific capacity of 920 mA h g-1 after 1000 cycles at a current density of 2 A g-1, indicating the advantages of the well-tailored structure. Additionally, the us-Si/C electrode can maintain an areal capacity of approximately 1.55 mA h cm-2 after 200 cycles at a high loading of 3.66 mg cm-2. Moreover, it presents practical applicability when assembled into LFP (lithium iron phosphate)//us-Si/C full cells. This preparation method presents great promise for achieving roll-to-roll manufacturing for practical applications due to its simplicity and efficiency.

The material-microorganism interface in microbial hybrid electrocatalysis systems

This review presents a comprehensive summary of the material-microorganism interface in microbial hybrid electrocatalysis systems. Microbial hybrid electrocatalysis has been developed to combine the advantages of inorganic electrocatalysis and microbial catalysis. However, electron transfer at the interfaces between microorganisms and materials is a very critical issue that affects the efficiency of the system. Therefore, this review focuses on the electron transfer at the material-microorganism interface and the strategies for building efficient microorganism and material interfaces. We begin with a brief introduction of the electron transfer mechanism in both the bioanode and biocathode of bioelectrochemical systems to understand the material-microorganism interface. Next, we summarise the strategies for constructing efficient material-microorganism interfaces including material design and modification and bacterial engineering. We also discuss emerging studies on the bio-inorganic hybrid electrocatalysis system. Understanding the interface between electrode/active materials and the microorganisms, especially the electron transfer processes, could help to drive the evolution of material-microorganism hybrid electrocatalysis systems towards maturity.

Highly selective electrosynthesis of H2O2 by N, O co-doped graphite nanosheets for efficient electro-Fenton degradation of p-nitrophenol

The activity and selectivity of the cathode towards electrosynthesis of H₂O₂ are critical for electro-Fenton process. Herein, nickel-foam modified with N, O co-doped graphite nanosheets (NO-GNSs/Ni-F) was developed as a cathode for highly efficient and selective electrosynthesis of H₂O₂. Expectedly, the accumulation of H₂O₂ at pH= 3 reached 494.2 mg L^-1 h^-1, with the selectivity toward H₂O₂ generation reaching 93.0%. The synergistic effect of different oxygen-containing functional groups and N species on the performance and selectivity of H₂O₂ electrosynthesis was investigated by density functional theory calculations, and the combination of epoxy and graphitic N (EP + N) was identified as the most favorable configuration with the lowest theoretical overpotential for H₂O₂ generation. Moreover, NO-GNSs/Ni-F was applied in the electro-Fenton process for p-nitrophenol degradation, resulting in 100% removal within 15 min with the kinetic rate constant of 0.446 min^-1 and 97.6% mineralization within 6 h. The efficient removal was mainly attributed to the generation of bulk ·OH. Furthermore, NO-GNSs/Ni-F exhibited excellent stability. This work provides a workable option for the enhancement of H₂O₂ accumulation and the efficient degradation of pollutants in electro-Fenton system.