Electrochemical Reduction Of O2 Research Articles

A Selective Copper Based Oxygen Reduction Catalyst for the Electrochemical Synthesis of H2O2 at Neutral pH.

H2O2 is a bulk chemical used as “green” alternative in a variety of applications, but has an energy and waste intensive production method. The electrochemical O2 reduction to H2O2 is viable alternative with examples of the direct production of up to 20% H2O2 solutions. In that respect, we found that the dinuclear complex Cu2(btmpa) (6,6’‐bis[[bis(2‐pyridylmethyl)amino]methyl]‐2,2’‐bipyridine) reduces O2 to H2O2 with a selectivity up to 90 % according to single linear sweep rotating ring disk electrode measurements. Microbalance experiments showed that complex reduction leads to surface adsorption thereby increasing the catalytic current. More importantly, we kept a high Faradaic efficiency for H2O2 between 60 and 70 % over the course of 2 h of amperometry by introducing high potential intervals to strip deposited copper (depCu). This is the first example of extensive studies into the long term electrochemical O2 to H2O2 reduction by a molecular complex which allowed to retain the high intrinsic selectivity of Cu2(btmpa) towards H2O2 production leading to relevant levels of H2O2.

Chemical and Electrochemical O2 Reduction on Earth-Abundant M-N-C Catalysts and Implications for Mediated Electrolysis.

M-N-C catalysts, incorporating non-precious-metal ions (e.g. M = Fe, Co) within a nitrogen-doped carbon support, have been the focus of broad interest for electrochemical O2 reduction and aerobic oxidation reactions. The present study explores the mechanistic relationship between the O2 reduction mechanism under electrochemical and chemical conditions. Chemical O2 reduction is investigated via the aerobic oxidation of a hydroquinone, in which the O-H bonds supply the protons and electrons needed for O2 reduction to water. Mechanistic studies have been conducted to elucidate whether the M-N-C catalyst couples two independent half-reactions (IHR), similar to electrode-mediated processes, or mediates a direct inner-sphere reaction (ISR) between O2 and the organic molecule. Kinetic data support the latter ISR pathway. This conclusion is reinforced by rate/potential correlations that reveal significantly different Tafel slopes, implicating different mechanisms for chemical and electrochemical O2 reduction.

Electrochemically produced local pH changes stimulating (bio)molecule release from pH-switchable electrode-immobilized avidin-biotin systems.

Immobilized avidin-biotin complexes were used to release biotinylated (bio)molecules upon producing local pH changes near an electrode surface by electrochemical reactions. The nitro-avidin complex with biotin was dissociated by increasing local pH with electrochemical O2 reduction. The avidin complex with iminobiotin was split by decreasing local pH with electrochemical oxidation of ascorbate. Both studied systems were releasing molecule cargo species in response to small electrical potentials (-0.4 V or 0.2 V for the O2 reduction or ascorbate oxidation, respectively) applied on the modified electrodes.

Non-precious metal electrocatalysts for two-electron oxygen electrochemistry: Mechanisms, progress, and outlooks

Hydrogen peroxide (H2O2) is a valuable chemical for a wide variety of applications. The environmentally friendly production route of the electrochemical reduction of O2 to H2O2 has become an attractive alternative to the traditional anthraquinone process. The efficiency of electrosynthesis process depends considerably on the availability of cost-effective catalysts with high selectivity, activity, and stability. Currently, there are many outstanding issues in the preparation of highly selective catalysts, the exploration of the interface electrolysis environment, and the construction of electrolysis devices, which have led to extensive research efforts. Distinct from the existing few comprehensive review articles on H2O2 production by two-electron oxygen reduction, the present review first explains the principle of the oxygen reduction reaction and then highlights recent advances in the regulation and control strategies of different types of catalysts. Key factors of electrode structure and device design are discussed. In addition, we highlight the promising co-production combination of this system with renewable energy or energy storage systems. This review can help introduce the potential of oxygen reduction electrochemical production of high-flux H2O2 to the commercial market.

Natural bamboo-derived O-doped rocky electrocatalyst for high-efficiency electrochemical reduction of O2 to H2O2

The in-situ H2O2 electrosynthesis by two-electron oxygen reduction reaction employing renewable electricity is a promising alternative to traditional anthraquinone process due to its security, environmental friendliness and excellent cost effectiveness, which requires high-performance, cost-effective and environmental-friendly electrocatalysts. A bamboo-derived O-doped rocky electrocatalyst is developed by facile pyrolysis and acid treatment for high-efficiency electroreduction of O2 to H2O2. Three-dimensional interconnected hierarchical pores in rocky electrocatalysts expose abundant electroactive sites and facilitate mass transfer of reaction species. From the results of rotating ring-disk electrode test, a H2O2 selectivity up to 80% and superior electrocatalytic activity of the prepared electrocatalyst are achieved by surface oxygen functionalization induced by acid treatment. At the optimal catalyst loading of 2 mg cm−2, prominent H2O2 productivity of 1037 mmol gcatalyst−1h−1 with high current efficiency up to 74.1% is achieved at 30 mA cm−2 by air-breathing cathode. Higher H2O2 productivity (1525 mmol gcatalyst−1h−1) is yielded by further raising the current density to 50 mA cm−2. Moreover, the durability test of the cathode through ten consecutive runs demonstrates its great stability for electrocatalytic generation of H2O2. This work inspires the development of promising biomass-derived electrocatalysts for green and sustainable on-site H2O2 electrosynthesis.

Hybrids of Reduced Graphene Oxide Aerogel and CNT for Electrochemical O2 Reduction

Carbon nanotubes (CNTs), graphene aerogels (GAs), and their hybrid (CNT-GA) prepared by hydrothermal treatment were tested in the electrocatalytic oxygen reduction reaction (ORR). The importance of porous structure derived from the combination of mesoporosity coming from CNTs with macroporosity stemming from GAs was evidenced because the hybrid carbon material exhibited synergistic performance in terms of kinetic current and onset potential. Different electrocatalysts were prepared based on these hybrids doped with nitrogen using different precursors and also supporting Fe nanoparticles. N-doped carbon hybrids showed higher electrocatalytic activity than their undoped counterparts. Nevertheless, both doped and undoped materials provided a mixed two and four electron reduction. On the other hand, the addition of a Fe precursor and phenanthroline to the CNT-GA allowed preparing an N-doped hybrid containing Fe nanoparticles which favored the 4-electron oxygen reduction to water, thus being an excellent candidate as a structured cathode in fuel cells.

Benzoporphyrin‐Based Nanocomposites for Photoelectrochemical O2 Reduction

AbstractThis research presents a new series of tetrabenzoporphyrins (TBPs) bearing p‐diphenylaminophenylethynyl and p‐carboxylphenylethynyl groups or two p‐carboxylphenylethynyl groups in a trans‐fashion on a TBP core for photoelectrochemical O2 reduction. Impact of electron‐donating diphenylamino and electron‐withdrawing surface‐anchoring carboxyl groups on photophysical and electrochemical properties of the target TBPs was experimentally and theoretically investigated in comparison with those of their benchmark analog. The results show that while the p‐carboxylphenylethynyl group give an electronic contribution to the molecules by lowering energy gap, the role of the p‐diphenylaminophenylethynyl group is found to be trivial. Preliminary investigation on electrochemical O2 reduction indicates significant catalytic activities of TBP‐modified TiO2/fluorene‐doped tin oxide electrodes at potentials of −0.2 V and −0.3 V vs. normal hydrogen electrode (NHE) in a pH‐neutral and ambient aqueous condition, leading to H2O2 formation. Upon photoirradiation, catalytic performance of such TBP‐based electrodes is further enhanced with the optimum yield obtained when the dicarboxyl derivatives and the potential of −0.3 V vs. NHE are applied. Proposed photoinjection mechanism of the dye/TiO2 simulated by time‐dependent density functional theory calculations supported the experimental results indicating the favorable role of the target TBPs as photoelectrocatalysts in the O2 reduction.

How determinant is the iron precursor ligand in Fe-N-C single-site formation and activity for oxygen reduction reaction?

Metal-Nitrogen-Carbon (M-N-C) materials have emerged as one of the best non-PGM alternatives to Pt/C catalysts for the electrochemical reduction of O2 in fuel cells. In this work, we explore how decisive is the iron precursor ligand in the Fe-Nx site formation when a commercial carbon black (Vulcan XC72) is pyrolyzed in the presence of an iron complex. Iron complexes coordinating different nitrogen ligands such as phthalocyanine, 1,10-Phenanthroline, 2,2’-Bipyridyl, imidazole, EDTA, etc., were tested. Different Fe-N-C catalysts were synthetized by using twelve different complexes to achieve a better understanding on the role of ligands on site formation and activity, i.e. the site density (SD) and the turn-over frequency (TOF), respectively. It was found that Fe-Nx active site can be effectively formed only when ligands containing aromatic nitrogen rings are used and that the ligand decomposition leads to a substantial change in the carbon morphology developing an increased micropore volume, while mesopore surface area is reduced. The activity was checked in both acidic and alkaline electrolyte by RRDE technique showing that the catalytic activity deeply depends on the type of iron complex, even if such difference is much less important when KOH was used as electrolyte. Site density was determined according to nitrite stripping method, and it was found that the activity (E1/2) in sulphuric acid electrolyte well correlate with the SD, which reaches its maximum when Fe(phen)3Cl2 was used as precursor (SD = 4.24 × 1018 sites g−1; TOF = 6.66 e− sites−1 s−1). Indeed, Fe(phen)3Cl2 involves on one hand a higher mesopore occlusion (from 93 to 34 m2 g−1), but on the other hand the etching due to the small molecules developed by the pyrolysis of the ligand leads to higher micropore surface (from 132 to 246 m2 g−1), which is an important aspect for the formation of Fe-Nx active sites. This clearly places a limit on the ability to increase catalytic activity simply by playing on the initial content of complex, since while we try to increase the SD by increasing the complex loading at the same time the textural properties worsen.Stability test and post-stress test site density analysis on the best catalysts show a higher stability in alkaline electrolyte. In acid electrolyte, the kinetic current decreases by 60% after 7000 cycles and this was proven to depends by the decreasing of the SD, attesting the labile nature of Fe-Nx sites when used in demanding conditions.

Tuning Coal into Graphene-Like Nanocarbon for Electrochemical H2O2 Production with Nearly 100% Faraday Efficiency

Electrochemical reduction of O2 to produce H2O2 provides the most promising alternative to the current anthraquinone process, whereas an electrocatalyst that is cost-effective and has rich resources, excellent oxygen reduction reaction (ORR) activity, and dominant two-electron (2e–) selectivity is highly required. Herein, by using inexpensive and earth-abundant anthracite coal as the precursor along with the KOH activation method, a defective graphene-like carbon (DGLC) nanomaterial has been successfully constructed. The as-prepared DGLC material features a graphene-like morphology, a hierarchical porous structure, a high surface area, abundant defects/edges, and a high content of ether functional groups, which endow it with excellent ORR activity, dominant 2e– selectivity, and high stability toward H2O2 synthesis in alkaline media. Remarkably, when employed as the electrocatalyst in H-cell, it can achieve a high H2O2 production rate of 355.0 mmol L–1 h–1 cm–2 gcat–1 with nearly 100% Faraday efficiency, which is superior to most carbon-based ORR catalysts. Experimental and theoretical studies describe that such high ORR activity and selectivity of DGLC are highly associated with its defect degree and ether groups (C–O–C) content, respectively, which contribute together to boost the superior 2e– ORR performance. This finding will be very helpful for designing a carbon-based 2e– ORR electrocatalyst toward H2O2 synthesis.

Electrochemiluminescence Imaging for High Throughput Analysis of Spheroids

Introduction Three-dimensional cultured cells, such as spheroids are believed to be promising models for drug screening and regenerative medicine because they effectively mimic the cellular response and metabolic activity in physiological contexts. To further study their functions for applications in clinical contexts, high-throughput analysis of living spheroids is required. To electrochemically evaluate cellular activity of spheroids, scanning electrochemical microscopy (SECM) has been widely used1; with the shortcomings of low through put and complicated control of scanning a probe. Another strategy utilized electrode array devices to this end2, although the spatial resolution is limited by the numbers and sizes of integrated electrodes. Here, we present electrochemiluminescence (ECL) imaging system for evaluation of cellular activity of 3D cell spheroids. ECL is an optical technique that utilizes electrochemical reaction to produce luminescence, and widely used in bioanalytical field. The unique features of ECL such as simple setups and temporal controllability of light emission are favorable for analysis of cells and molecules derived from cells. However, there is few studies which apply ECL for imaging of 3D cell spheroids. L-012, a luminol analog was used for ECL luminophore, which emits strong luminescence in the presence of H2O2. In the proposed system, H2O2 was generated in situ by electrochemical reduction of O2, former to the electrochemical oxidation of L-012. Owing to the electrochemical reduction of O2 to H2O2, efficient luminescence of L-012 was obtained. Moreover, as living cell spheroids consume O2 to maintain cellular activity, the electrochemical reduction of O2 is hindered at the peripheral environment of a spheroid, resulting with decrease in luminescence around the spheroid. Thus, the distribution of ECL suppression indicates the respiratory activity of a spheroid. To demonstrate feasibility of the proposed ECL system, the respiratory activity of mesenchymal stem cell (MSC) spheroids was measured either with ECL imaging and SECM. Finally, time-lapse and multiple imaging of the cellular activity of the living MSC spheroids were demonstrated in the ECL imaging. Experimental The ECL system was composed of an Au substrate as a working electrode, an Ag/AgCl and a Pt wire as a reference and counter electrode, respectively. A chamber made of polydimethylsiloxane (PDMS) was bonded on the Au substrate. The electrodes were connected to a potentiostat and mounted on a stereomicroscope. To demonstrate ECL imaging of cell activities, human mesenchymal stem cells (hMSCs) were prepared. For fabrication of spheroids, the MSCs were seeded at 2×105 cells per well in a 96-well U-bottom plate in DMEM. MSC spheroids were formed within 48 h and the half of the spheroids were induced to chondrogenic differentiation by commercial differentiation medium subsequently. For ECL imaging, 200 mM L-012 solution (PBS, pH 7.4) was introduced to the chamber, and spheroids were settled on the substrate using a micropipette. A potential of -0.3 V was applied for 30 s to generate H2O2, followed by +0.7 V for 30 s to oxidize L-012. During the potential apply, ECL images were taken by a digital camera with 30 s of exposure time. For the time-lapse imaging, multiple spheroids were introduced on the Au electrode at once and ECL imaging was conducted 2–60 min after they settled. Results and discussion In the ECL images of MSC spheroids, the bodies of the spheroids displayed bright emission, possibly due to the compacted spherical structure of the spheroids that scattered light from ECL. At the living spheroid, the circumference of the spheroid became dark, indicating that the ECL was suppressed due to O2 consumption of the spheroid. In fact, there was no suppression of ECL around fixed spheroids as there was no respiratory activity in those cells. Interestingly, in comparison with the control and differentiation induced spheroids, the decline of the ECL intensity was larger in the latter spheroid indicating inherent respiratory activity among induction of the differentiation. With the ECL images, the respiratory activity of the spheroids was calculated by quantifying the distribution of ECL intensity around the spheroid. The results corresponded well with that measured by SECM. The time-lapse ECL imaging of multiple MSC spheroids displayed subtle changes in the respiratory activity of the spheroids during observation. When the spheroids were removed from the electrode after 60 min, the area right under the spheroids remained slightly dark, indicating cellular components or metabolites might have adsorbed on the electrode surface. Overall, the ECL system enabled simultaneous analysis of cellular activity of multiple spheroids with good resolution comparable with that of SECM, while the measurement time was highly improved with a single flat electrode for ECL reaction. References Kaoru Hiramoto et al., Electrochim. Acta, 340, 135979, (2020)Kosuke Ino et al., Electrochim. Acta, 268, 554-561, (2018)

Mechanistic Study of the Activation and the Electrocatalytic Reduction of Hydrogen Peroxide by Cu-tmpa in Neutral Aqueous Solution.

Hydrogen peroxide plays an important role as an intermediate and product in the reduction of dioxygen by copper enzymes and mononuclear copper complexes. The copper(II) tris(2‐pyridylmethyl)amine complex (Cu‐tmpa) has been shown to produce H2O2 as an intermediate during the electrochemical 4‐electron reduction of O2. We investigated the electrochemical hydrogen peroxide reduction reaction (HPRR) by Cu‐tmpa in a neutral aqueous solution. The catalytic rate constant of the reaction was shown to be one order of magnitude lower than the reduction of dioxygen. A significant solvent kinetic isotope effect (KIE) of 1.4 to 1.7 was determined for the reduction of H2O2, pointing to a Fenton‐like reaction pathway as the likely catalytic mechanism, involving a single copper site that produces an intermediate copper(II) hydroxo species and a free hydroxyl radical anion in the process.

Electrochemical Reduction of O2 in Ca2+ -Containing DMSO: Role of Roughness and Single Crystal Structure.

In this study, the oxygen reduction reaction (ORR) in Ca2+‐containing dimethyl sulfoxide (DMSO) at well‐ordered and rough electrode surfaces is compared by using cyclic voltammetry, differential electrochemical mass spectrometry, rotating ring disk electrode, and atomic force microscopy measurements. Slightly soluble CaO2 is the main product during early ORR on gold electrodes; after completion of a monolayer of CaO and/or CaO2, which is formed in parallel and in competition to the peroxide, only superoxide is formed. When the monolayer is completely closed on smooth annealed Au, no further reduction occurs, whereas on rough Au a defect‐rich layer allows for continuous formation of superoxide. CaO2 formed either via two subsequent 1 e- transfer steps or by disproportionation of superoxide may be deposited on top of the CaO/CaO2 adsorbate layer. The slow dissolution of the peroxide particles is demonstrated by AFM. Whereas a smooth CaO/CaO2‐covered electrode shows severe deactivation and a CaO/CaO2‐covered rough electrode allows for diffusion‐limited superoxide formation, on single crystals peroxide formation is more pronounced. The reason is most likely the lack of nucleation sites for the blocking CaO/CaO2 layer. RRDE investigations showed sluggish reoxidation kinetics of the dissolved peroxide, which are most likely due to ion pairing with Ca2+. The apparent transfer coefficient is estimated by using variation of the electrode roughness, confirming the result of the usual Tafel analysis and indicating an equilibrated first 1 e- transfer.

Effects of the induced micro- and meso-porosity on the single site density and turn over frequency of Fe-N-C carbon electrodes for the oxygen reduction reaction

Fe-N-C have emerged as one of the best non-PGM alternatives to Pt/C catalysts for the electrochemical reduction of O2 in fuel cells. In this work, we explore the effect of steam and CO2 treatments at high temperatures on the nanometric porous structure of a commercial carbon black. Using those support materials, we synthesize different Fe-N-C catalysts to achieve a better understanding on the role of micro- and mesopores of the support towards catalytic site formation and site activity. Different time and temperature of treatments result in an almost linear increment of surface area and microporous volume, which allows better nitrogen functionalization. Site density evaluation, performed using a recently described NO-stripping technique, showed an increase in site density and TOF which correlates well with the morphology variation. The percentage of active iron increases from 2.65 % to 14.74 % in activated catalysts confirming a better access of electrolyte to the iron sites.

Efficient Discovery of Active, Selective, and Stable Catalysts for Electrochemical H2O2 Synthesis through Active Motif Screening

Electrochemical reduction of O2 provides a clean and decentralized pathway to produce H2O2 compared to the current energy-intensive anthraquinone process. As the electrochemical reduction of O2 pro...

Promoting of direct electron transfer of multicopper oxidase by control of enzyme molecule density on multi-walled carbon nanotube

In order to improve the performance of direct electron transfer-type electrode using multicopper oxidase (MCO), it is important to shorten the distance between the redox site of the enzyme and the electrode surface to increase electron transfer efficiency between enzyme and electrode. In this study, we focused on the mobility of the MCO from hyperthermophilic archaeon, Pyrobaculum aerophilum, immobilized onto electrode surface via an affinity tag at the MCO terminus. The mobility of the immobilized enzyme was controlled by changing the density of the immobilized enzyme on the electrode surface by altering the density of the linker for enzyme immobilization. The electrode with low density of MCO immobilized on electrode surface was improved swing ability of the enzyme. It showed 265% higher current density for electrochemical O2 reduction than that with high density of MCO immobilized on electrode surface. Biofuel cell using a cathode with a low density of MCO immobilized on the electrode showed 160% higher power density than a biofuel cell using a cathode with a high density of MCO immobilized on the electrode.

Electrochemical conversion pathways and existing morphology of arsenic(III) in anode-cathode separated electrolytic cells

Abstract To explore the electrochemical conversion of arsenic at different voltages and pH, an open separated electrolytic cell with a platinum anode and a graphite cathode was selected for this paper. The form and concentration of arsenic in the anodic cell and cathodic cell were detected. Experimental results proved that at 40.0 V, As(III) in an acid electrolyte in the cathodic cell was firstly mainly reduced to AsH3 with trace As(0) as intermediate. As the electrolysis time arrived at 27 min, pH in the cathodic cell jumped suddenly from acidity to alkalinity, accompanied by the majority of the remaining As(III) converting to As(V) for an instant. As time went on, As(III) and As(V) remained almost unchanged at the ratio of 1:3, and the reduction of As(III) became extremely weak in the alkaline environment. When pH in the cathodic tank was adjusted to keep it acid, As(III) was eventually converted to AsH3. Compared with high voltage, at a low voltage of 1.0 V the cathode failed to achieve the potential of As(III) reduction and As(III) was eventually oxidized to As(V) in the acid catholyte. Electrochemical oxidation of As(III) in the open cathodic cell was likely caused by in-situ generation of peroxide from electrochemical reduction of O2. Theoretical support for electrochemical oxidation of As(III) on a carbon cathode in neutral and weak alkaline media is provided in this study.

Nitrogen and Oxygen Co-Doping Assisted Synthesis of Highly Dispersed Pd Nanoparticles on Hollow Carbon Spheres as Efficient Electrocatalysts for Oxygen Reduction Reaction.

Electrochemical reduction of O2 (oxygen reduction reaction; ORR) provides an opportunity to achieve the commercial application of clean energy, but it remains challenging, so the rational design of inexpensive and efficient electrocatalysts is required. Palladium-based electrocatalysts have emerged as a class of the most promising candidates for the ORR, which could accelerate O2 adsorption, dissociation, and electron transfer. However, the metal Pd atoms tend to aggregate into nanoparticles, driven by the tendency of the metal surface free energy to decrease, which significantly reduces the atom utilization efficiency and the catalytic performance. Herein, a facile double solvent impregnation method is developed for the synthesis of highly dispersed Pd nanoparticles supported on hollow carbon spheres (Pd-HCS), which could act as efficient electrocatalysts for the ORR in basic solution. Systematic investigation reveals that the nitrogen-containing and oxygen-containing functional groups (especially -COOH groups) are essential for achieving the homogenous dispersion of Pd nanoparticles. Significantly, the optimized Pd-HCS electrocatalyst with homogeneously dispersed Pd nanoparticles and Pd-N sites delivers high electrocatalytic activity for the ORR and excellent stability, without significant decay in onset potential and half-potential and good resistance to methanol crossover. This work offers a new route for the rational design of efficient ORR electrocatalysts toward advanced materials and emerging applications.

Catalytic C-H Bond Oxidation Using Dioxygen by Analogues of Heme Superoxide.

Heme active sites are capable of oxidizing organic substrates by four electrons using molecular oxygen (heme dioxygenases), where a dioxygen (O2) adduct of heme (FeIII-O2•-) acts as the primary oxidant, in contrast to monooxygenases, where high-valent species are involved. This chemistry, although lucrative, is difficult to access using homogeneous synthetic systems. Over the past few years using a combination of self-assembly and in situ resonance Raman spectroscopy, the distribution of different reactive intermediates formed during the electrochemical reduction of oxygen has been elucidated. An FeIII-O2•- species, which is the reactive species of dioxygenase, is an intermediate in heterogeneous electrochemical O2 reduction by iron porphyrins and its population, under electrochemical conditions, may be controlled by controlling the applied potential. Iron porphyrins having different axial ligands are constructed on a self-assembled monolayer of thiols on an electrode, and these constructs can activate O2 and efficiently catalyze the dioxygenation of 3-methylindole and oxidation of a series of organic compounds having C-H bond energies between 80 and 90 kcal mol-1 at potentials where FeIII-O2•- species are formed on the electrode. Isotope effects suggest that hydrogen-atom transfer from the substrate is likely to be the rate-determining step. Axial thiolate ligands are found to be more efficient than axial imidazoles or phenolates with turnover numbers above 60000 and turnover frequencies over 60 s-1. These results highlight a new reaction engineering approach to harness O2 as a green oxidant for efficient chemical oxidation.

Tailoring Selectivity of Electrochemical Hydrogen Peroxide Generation by Tunable Pyrrolic‐Nitrogen‐Carbon

AbstractThe electrochemical reduction of O2 via a two‐electron reaction pathway to H2O2 provides a possibility for replacing the current anthraquinone process, enabling sustainable and decentralized H2O2 production. Here, a nitrogen‐rich few‐layered graphene (N‐FLG) with a tunable nitrogen configuration is developed for electrochemical H2O2 generation. A positive correlation between the content of pyrrolic‐N and the H2O2 selectivity is experimentally observed. The critical role of pyrrolic‐N is elucidated by the variable intermediate adsorption profiles as well as the dependent negative shifts of the pyrrolic‐N peak on X‐ray adsorption near edge structure spectra. By virtue of the optimized N doping configuration and the unique porous structure, the as‐fabricated N‐FLG electrocatalyst exhibits high selectivity toward electrochemical H2O2 synthesis as well as superior long‐term stability. To achieve high‐value products on both the anode and cathode with optimized energy efficiency, a practical device coupling electrochemical H2O2 generation and furfural oxidation is assembled, simultaneously enabling a high yield rate of H2O2 at the cathode (9.66 mol h−1 gcat−1) and 2‐furoic acid at the anode (2.076 mol m−2 h−1) under a small cell voltage of 1.8 V.

Bimodal Heterogeneous Functionality in Redox-Active Conjugated Microporous Polymer toward Electrocatalytic Oxygen Reduction and Photocatalytic Hydrogen Evolution.

The designing and development of heterogeneous catalysts for conversion of renewable energy to chemical energies by electrochemical as well as photochemical processes is at the forefront of energy research. In this work, two new donor-acceptor-based redox-active conjugated microporous polymers (CMPs) (TAPA-OPE-mix and TAPA-OPE-gly) are synthesized through Schiff base condensation reaction using a microwave synthesizer. Notably, the asymmetric and symmetric bola-amphiphilic nature of the OPE struts results in distinct nanostructuring and morphologies in the CMPs. Interestingly, both CMPs show impressive heterogeneous catalytic activity toward electrochemical O2 reduction and photocatalytic H2 evolution reactions, and therefore, act as bimodal electro- and photocatalytic porous organic materials. Furthermore, the redox-active property of the CMPs is exploited for in situ generation and stabilization of platinum nanoparticles (Pt), and these Pt@CMPs exhibit significantly enhanced photocatalytic activity.