Highly efficient electrochemical production of hydrogen peroxide over nitrogen and phosphorus dual-doped carbon nanosheet in alkaline medium

Catalytically Active Carbon for Oxygen Reduction Reaction in Energy Conversion: Recent Advances and Future Perspectives

The shortage and unevenness of fossil energy sources are affecting the development and progress of human civilization. The technology of efficiently converting material resources into energy for utilization and storage is attracting the attention of researchers. Environmentally friendly biomass materials are a treasure to drive the development of new-generation energy sources. Electrochemical theory is used to efficiently convert the chemical energy of chemical substances into electrical energy. In recent years, significant progress has been made in the development of green and economical electrocatalysts for oxygen reduction reaction (ORR). Although many reviews have been reported around the application of biomass-derived catalytically active carbon (CAC) catalysts in ORR, these reviews have only selected a single/partial topic (including synthesis and preparation of catalysts from different sources, structural optimization, or performance enhancement methods based on CAC catalysts, and application of biomass-derived CACs) for discussion. There is no review that systematically addresses the latest progress in the synthesis, performance enhancement, and applications related to biomass-derived CAC-based oxygen reduction electrocatalysts synchronously. This review fills the gap by providing a timely and comprehensive review and summary from the following sections: the exposition of the basic catalytic principles of ORR, the summary of the chemical composition and structural properties of various types of biomass, the analysis of traditional and the latest popular biomass-derived CAC synthesis methods and optimization strategies, and the summary of the practical applications of biomass-derived CAC-based oxidative reduction electrocatalysts. This review provides a comprehensive summary of the latest advances to provide research directions and design ideas for the development of catalyst synthesis/optimization and contributes to the industrialization of biomass-derived CAC electrocatalysis and electric energy storage.

Recent advances in electrosynthesis of H2O2via two-electron oxygen reduction reaction

The electrosynthesis of hydrogen peroxide (H2O2) via a selective two-electron oxygen reduction reaction (2e- ORR) presents a green and low-energy-consumption alternative to the traditional, energy-intensive anthraquinone process. This review encapsulates the principles of designing relational electrocatalysts for 2e- ORR and explores remaining setups for large-scale H2O2 production. Initially, the review delineates the fundamental reaction mechanisms of H2O2 production via 2e- ORR and assesses performance. Subsequently, it methodically explores the pivotal influence of microstructures, heteroatom doping, and metal hybridization along with setup configurations in achieving a high-performance catalyst and efficient reactor for H2O2 production. Thereafter, the review introduces a forward-looking methodology that leverages the synergistic integration of catalysts and reactors, aiming to harmonize the complementary characteristics of both components. Finally, it outlines the extant challenges and the promising avenues for the efficient electrochemical production of H2O2, setting the stage for future research endeavors.

Encapsulation of Co nanoparticles with single-atomic Co sites into nitrogen-doped carbon for electrosynthesis of hydrogen peroxide

The electrosynthesis of hydrogen peroxide (H2O2) offers a sustainable and viable option for generating H2O2 directly, as an alternative to the anthraquinone oxidation method. This study focuses on the comparative study of Co nanoparticles and single-atomic Co sites (Co SACs) that were encapsulated into nitrogen-doped carbon for the electrosynthesis of H2O2, which has been synthesized by direct pyrolysis of Zn/Co-ZIF or Co-based zeolitic imidazolate frameworks (ZIF-67). The electrochemical measurement results demonstrate that the coexistence of Co nanoparticles and single-atomic Co sites in the CoNC catalyst is more conducive for H2O2 production compared to Co SACs only, possessing better H2O2 selectivity of 73.3% and higher faradaic efficiency of 87%. The improved performance of CoNC with SACs can be attributed to the presence of additional Co nanoparticles in the nitrogen-doped carbon layers.

Electrochemical production of hydrogen peroxide by non-noble metal-doped g-C3N4 under a neutral electrolyte

Electrochemical oxygen reduction (ORR) for the production of clean hydrogen peroxide (H2O2) is an effective alternative to industrial anthraquinone methods. The development of highly active, stable, and 2e- ORR oxygen reduction electrocatalysts while suppressing the competing 4e- ORR pathway is currently the main challenge. Herein, bimetallic doping was successfully achieved based on graphitic carbon nitride (g-C3N4) with the simultaneous introduction of K and Co, whereby 2D porous K-Co/CNNs nanosheets were obtained. The introduction of Co promoted the selectivity for H2O2, while the introduction of K not only promoted the formation of 2D nanosheets of g-C3N4, but also inhibited the ablation of H2O2 by K-Co/CNNs. Electrochemical studies showed that the selectivity of H2O2 in K-Co/CNNs under neutral electrolyte was as high as 97%. After 24 h, the H2O2 accumulation of K-Co/CNNs was as high as 31.7 g L-1. K-Co/CNNs improved the stability of H2O2 by inhibiting the ablation of H2O2, making it a good 2e- ORR catalyst and providing a new research idea for the subsequent preparation of H2O2.

Facilitating two-electron oxygen reduction with pyrrolic nitrogen sites for electrochemical hydrogen peroxide production

Electrocatalytic hydrogen peroxide (H₂O₂) production via the two-electron oxygen reduction reaction is a promising alternative to the energy-intensive and high-pollution anthraquinone oxidation process. However, developing advanced electrocatalysts with high H₂O₂ yield, selectivity, and durability is still challenging, because of the limited quantity and easy passivation of active sites on typical metal-containing catalysts, especially for the state-of-the-art single-atom ones. To address this, we report a graphene/mesoporous carbon composite for high-rate and high-efficiency 2e^- oxygen reduction catalysis. The coordination of pyrrolic-N sites -modulates the adsorption configuration of the *OOH species to provide a kinetically favorable pathway for H₂O₂ production. Consequently, the H₂O₂ yield approaches 30 mol g^-1 h^-1 with a Faradaic efficiency of 80% and excellent durability, yielding a high H₂O₂ concentration of 7.2 g L^-1. This strategy of manipulating the adsorption configuration of reactants with multiple non-metal active sites provides a strategy to design efficient and durable metal-free electrocatalyst for 2e^- oxygen reduction.

The composite of bismuth oxyiodide-bismuth/nitrogen-doped carbon for photoreduction and electrochemical/photoelectrochemical dual-model sensing of Cr(VI)

A porous bismuth oxyiodide-metal bismuth/nitrogen-doped carbon (BiOI-Bi/N-C) composite composed of BiOI nanosheets, N-C sheets, and metallic Bi nanoparticles was prepared. BiOI-Bi/N-C exhibited remarkable cathodic photoelectrochemical activity and rapid adsorption capacity for Cr(VI) ions. Interestingly, the photocatalytic process of BiOI-Bi/N-C toward Cr(VI) was pH dependent. Under acidic medium, the synthesized material displayed efficient photocatalysis and achieved 95.0% photoreduction efficacy for Cr(VI) ions to Cr³⁺ within 30 min under visible light irradiation. Under neutral medium, Cr(VI) state showed a different photocatalytic process, and Cr(OH)₃ as a product covered on BiOI-Bi/N-C, which decreased the electrochemical (EC) and photoelectrochemical (PEC) performance of BiOI-Bi/N-C. Based on the findings, BiOI-Bi/N-C was utilized as EC/PEC dual-model sensing interface for the detection of Cr(VI) ions. The presented dual-model sensing method displayed an ultralow limit of detection down to 6.8 pM for EC and 3.2 pM for PEC. It demonstrated the practical application potential for the assay of Cr(VI) in real samples.

Influence of Nitrogen Doping into Carbon on the Activation Barrier of ORR in Alkaline Medium: An Investigation Based on Eyring Analysis

The oxygen reduction reaction (ORR) is investigated on metal-free carbon (Vulcan XC-72) and nitrogen-doped (∼≤1%) carbon (N/C-900) in 0.1 M KOH. The product distribution (O₂ to OH^- and HO₂^-) as a function of overpotential (η) in the temperature range of 293-323 K is analyzed using a rotating ring-disk electrode (RRDE) assembly. The kinetic current due to reduction of O₂ to HO₂^- is estimated and used in the Eyring analysis to determine the change in enthalpy of activation (ΔH^#). It is shown that doping of carbon with nitrogen (even with ≤1 wt %) causes substantial increase in the number of active sites (almost 2-fold) and reduction in ΔH^# at any η. Moreover, ΔH^# is a stronger function of η on N/C-900 as compared to that on the carbon surface.

Promotion of the Efficient Electrocatalytic Production of H2O2 by N,O- Co-Doped Porous Carbon

H₂O₂ generation via an electrochemical two-electron oxygen reduction (2e^- ORR) is a potential candidate to replace the industrial anthraquinone process. In this study, porous carbon catalysts co-doped by nitrogen and oxygen are successfully synthesized by the pyrolysis and oxidation of a ZIF-67 precursor. The catalyst exhibits a selectivity of ~83.1% for 2e^- ORR, with the electron-transferring number approaching 2.33, and generation rate of 2909.79 mmol g^-1 h^-1 at 0.36 V (vs. RHE) in KOH solution (0.1 M). The results prove that graphitic N and -COOH functional groups act as the catalytic centers for this reaction, and the two functional groups work together to greatly enhance the performance of 2e^- ORR. In addition, the introduction of the -COOH functional group increases the hydrophilicity and the zeta potential of the carbon materials, which also promotes the 2e^- ORR. The study provides a new understanding of the production of H₂O₂ by electrocatalytic oxygen reduction with MOF-derived carbon catalysts.

Bioinspired and Bioderived Aqueous Electrocatalysis

The development of efficient and sustainable electrochemical systems able to provide clean-energy fuels and chemicals is one of the main current challenges of materials science and engineering. Over the last decades, significant advances have been made in the development of robust electrocatalysts for different reactions, with fundamental insights from both computational and experimental work. Some of the most promising systems in the literature are based on expensive and scarce platinum-group metals; however, natural enzymes show the highest per-site catalytic activities, while their active sites are based exclusively on earth-abundant metals. Additionally, natural biomass provides a valuable feedstock for producing advanced carbonaceous materials with porous hierarchical structures. Utilizing resources and design inspiration from nature can help create more sustainable and cost-effective strategies for manufacturing cost-effective, sustainable, and robust electrochemical materials and devices. This review spans from materials to device engineering; we initially discuss the design of carbon-based materials with bioinspired features (such as enzyme active sites), the utilization of biomass resources to construct tailored carbon materials, and their activity in aqueous electrocatalysis for water splitting, oxygen reduction, and CO₂ reduction. We then delve in the applicability of bioinspired features in electrochemical devices, such as the engineering of bioinspired mass transport and electrode interfaces. Finally, we address remaining challenges, such as the stability of bioinspired active sites or the activity of metal-free carbon materials, and discuss new potential research directions that can open the gates to the implementation of bioinspired sustainable materials in electrochemical devices.

Recent advances in carbonaceous catalyst design for the in situ production of H2O2 via two-electron oxygen reduction

The electrochemical oxygen reduction reaction has received increasing attention as a relatively green, safe and sustainable method for in situ hydrogen peroxide (H₂O₂) production. Recently, significant achievements have been made to explore carbon-based (noble metal-free) low-cost and efficient electrocatalysts for H₂O₂ electroproduction, which could potentially replace the traditional anthraquinone process. However, to realize industrial-scale implementation, a highly active and selective catalytic material is needed. In this review paper, we first expound on the oxygen reduction reaction (ORR) mechanism, which is the origin of in situ H₂O₂ production. Then, the recent progress in the development of modified carbon-based catalysts is reviewed and classified, corresponding to their physical or chemical modulation. Furthermore, an overview is provided of the available examples from pilot/large-scale applications. Finally, an outlook on the current challenges and future research prospects to transfer the lab-developed catalysts into pilot or industrial-scale reactors is briefly discussed.