Electrocatalytic H2O2 Production Research Articles

Precise Design of Covalent Organic Frameworks for Electrocatalytic Hydrogen Peroxide Production.

Electrochemical synthesis of H2 O2 with high productivity is a significant challenge in electrocatalysis. Herein, we develop Mg-ion contained covalent organic frameworks (MgP-DHTA-COF), comprising stacked 2D layers, well-defined skeletons, and well-ordered monodispersed active sites, for the electrocatalytic production of H2 O2 directly from O2 and H2 O. The precise-designed MgP-DHTA-COF achieves H2 O2 selectivity up to 96%, high Faradaic efficiency of 91% and reliable stability for H2 O2 synthesis in 0.10 mol L-1 KOH aqueous solution. Both experiments and simulations demonstrate that the pyrrolic-N fixed Mg ions in the knots promote the reactivity of COF and enhance the adsorption ability of OOH*. This work provides a valuable example for the design of an efficient electrocatalyst based on COFs for H2 O2 production.

In Situ Deposition of Platinum-Group Metals for Electrocatalytic Hydrogen Peroxide Production By Oxygen Reduction

Hydrogen peroxide (H2O2) is a valuable commodity chemical that serves as a disinfectant for a number of important chemical end-use applications and as an oxidant for a several emerging technologies for oxidative chemical transformations. Recently there has been a resurgence of interest in the electrocatalytic production of H2O2 by oxygen reduction because it has been recognized to be compatible with the general concept of distributed chemical manufacturing, which in many cases presents strategic advantages over conventional operations based on centralized, large-scale systems. When compared with conventional synthesis technologies, electrocatalytic production of H2O2 – which uses only air, water, and electricity as inputs – is amenable to greater geographic distribution and shows strong potential to be cleaner and more sustainable.This presentation will describe efforts to utilize platinum-group metals as electrocatalysts for the cathodic reduction of O2 to H2O2 in water. Platinum-group metals are prototypical fuel cell catalysts and generally regarded to be non-selective to H2O2. The presented results will show that in certain electrodeposition synthesis conditions, these metals can form the basis of engineered electrodes that are both highly selective and active for cathodic H2O2 production by oxygen reduction. The use of these metals presents an engineering advantage because they are acid-stable, and therefore (1) compatible with existing PEM fuel cell cathode environments and (2) produce H2O2 in the low-pH environment where its stability is maximized. This presentation will discuss the physical, structure, and chemical properties of electrocatalysts that correlate with high H2O2 selectivity, and the fundamentals of the electrodeposition technique by which they are synthesized.

Biochar cathode: Reinforcing electro-Fenton pathway against four-electron reduction by controlled carbonization and surface chemistry

Porous biochars have attracted tremendous interests in electrochemical applications. In this study, a family of biochars were prepared from cellulose subject to different carbonization temperatures ranging from 400 to 700 °C, and the biochars were in-situ activated by a molten salt (ZnCl2) to construct a hierarchically porous architecture. The activated porous biochars (ZnBC) were used as a carbocatalyst for electro-Fenton (EF) oxidation of organic contaminants. Results showed that high-temperature carbonization improved the activity of biochar for four-electron oxygen reduction reaction (ORR) due to the rich carbon defects, while the mild-temperature treatment regulated the species and distribution of oxygen functional groups to increase the production of hydrogen peroxide (H2O2) via a selective two-electron ORR pathway. ZnBC-550 was the best cathode material with a high ORR activity without compromise in H2O2 selectivity; a high production rate of H2O2 (796.1 mg/g/h) was attained at −0.25 V vs RHE at pH of 1. Furthermore, Fe(II) addition induced an electro-Fenton system to attain fast decomposition of various organic pollutants at −0.25 V vs RHE (reversible hydrogen electrode) and pH of 3 with a satisfactory mineralization efficiency toward phenolic pollutants. The EF system maintains its excellent stability for 10 cycles. Hydroxyl radicals were identified as the dominant reactive oxygen species based on in situ electron paramagnetic resonance (EPR) analysis and radical quenching tests. This study gains new insights into electrocatalytic H2O2 production over porous biochars and provides a low-cost, robust and high-performance electro-Fenton cathode for wastewater purification.

Graphitic N in nitrogen-Doped carbon promotes hydrogen peroxide synthesis from electrocatalytic oxygen reduction

Electrocatalytic two-electron oxygen reduction reaction (2e− ORR) is a promising strategy to achieve hydrogen peroxide (H2O2) production, which can replace the anthraquinone method in industrial processes. Nitrogen-doped carbon materials are active and selective electrocatalysts for 2e− ORR; however, it remains challenging to develop N-doped carbons for practical H2O2 production and pinpoint the exact role of nitrogen functionalities. Here, we examine covalent organic framework-derived nitrogen-doped carbons with well-defined porous structure and tunable N species for electrocatalytic H2O2 production. Electrochemical studies show their highest ORR activity and H2O2 selectivity of up to 75% in alkaline electrolyte. Notably, chronoamperometric bulk electrolysis achieves an unprecedented carbon-catalyzed H2O2 yield rate of 1286.9 mmol gcatalyst−1 h−1 and a faradaic efficiency of 69.8% at pH 13. X-ray photoelectron spectroscopy analysis combined with control experiments reveals that graphitic N is responsible for H2O2 production from 2e− ORR on N-doped carbons. Our work provides insights into the rational development of heteroatom-doped carbon electrocatalysts for efficient H2O2 generation.

Solar hydrogen peroxide production on carbon nanotubes wired to titania nanorod arrays catalyzing As(III) oxidation

We present an off-grid, standalone electrocatalytic H2O2 production reaction (HPR) using carbon nanotubes (CNT) wired to hydrogen-treated TiO2 nanorod (h-TNR) arrays catalyzing the oxidation of As(III) to As(V) under simulated solar light (AM 1.5; 100 mW cm−2). Loading CNT onto acid-treated carbon paper (a-CP) significantly enhances the catalytic 2-electron transfer to O2, leading to a Faradaic efficiency (FE) of ∼100% for the HPR. To drive the HPR, the 2-electron oxidation of toxic As(III) to less toxic As(V) that accompanies the production of the proton/electron couples is achieved at an FE of >80% using the h-TNR arrays. The high FEs of the anodic and cathodic reactions are maintained over 10 h when a direct-current voltage of 0.7 V is applied to the h-TNR photoanode and CNT/a-CP cathode pair. The coupling of a mono-Si photovoltaic array that is one-tenth the size of h-TNR photoanode to the pair of h-TNR and CNT/a-CP successfully drives the standalone operation of both reactions at the high FEs (>90%). The surface characterization of the as-synthesized materials and the reaction mechanism are discussed in detail.

A novel electro-catalytic membrane contactor for improving the efficiency of ozone on wastewater treatment

A novel electro-catalytic membrane contactor was designed to break the two constrains in O3 wastewater treatment technology simultaneously: the mass transfer of O3-water and the decomposition rate of O3 into OH. In the electro-catalytic membrane contact ozonation (ECMCO) process, O2 and O3, in the gas chamber, diffuse through the hydrophobic membrane into the water phase; O2 is electro-reduced to H2O2 that catalyzes O3 producing OH to degrade organic compounds rapidly. The removal rate of nitrobenzene (NB) was significantly improved by the combination of membrane contactor and electro-catalytic process. The removal rates of NB in 120 min were 85%, 55% and 23% for ECMCO, membrane contact ozonation and electrolysis, respectively. O3 concentration and current density had positive effects on the removal of NB, which was related to the accumulated H2O2 concentration in aqueous phase. Gas flow had slight positive effects on NB removal when it was lower than 50 mL/min. The pH of the feed may affect the production and the form of H2O2 and hence the removal of NB. The highest removal rate in 120 min was up to 95.7% at the initial pH of 4.5. Mass transfer and electrolysis are synthetic in ECMCO process. On one hand, the mass transfer of O3 increased by 2 times due to the electro-catalytic production of H2O2. On the other hand, the existence of O3 promoted the production of H2O2. ECMCO has great potential on promoting mass transfer and decomposition of O3 into OH for the industrial application of O3.

Enhanced electrocatalytic production of H2O2 at Co-based air-diffusion cathodes for the photoelectro-Fenton treatment of bronopol

(Co, S, P)-decorated multiwalled carbon nanotubes (MWCNTs) have been synthesized following a hydrothermal route as electrocatalysts to manufacture large surface area air-diffusion cathodes with carbon cloth as substrate. The enhanced electrocatalytic H2O2 production as compared with Co-free MWCNTs cathodes was demonstrated in a 2.5-L pre-pilot plant with either a RuO2-based or boron-doped diamond (BDD) anode, accumulating between 2- and 3-fold greater H2O2 contents with the catalyzed cathode. The good stability of this new material was ensured from the low Co leaching, with less than 9% Co released to solutions upon repeated usage. Aqueous solutions of the brominated organic preservative bronopol with 0.050 M Na2SO4 at pH 3.0 were comparatively treated by electro-oxidation (EO-H2O2), electro-Fenton (EF), UVA-assisted photoelectro-Fenton (PEF) and solar PEF (SPEF) at constant current density. SPEF with BDD anode and the catalyzed cathode showed the best performance, with total bronopol removal at 210 min and 94% mineralization after 360 min at 40 mA cm−2, thanks to the action of OH, BDD(OH) and sunlight. Formic acid was identified as main reaction by-product, whereas Br and N atoms were mainly converted to Br–, BrO3– and NO3–. Some unidentified organic by-product containing Br and N was formed as well.

Optimization of electrocatalytic H2O2 production at pilot plant scale for solar-assisted water treatment

This manuscript summarizes the successful start-up and operation of a hybrid eco-engineered water treatment system, at pilot scale. The pilot unit, with 100 L capacity, has been devised for the efficient electrocatalytic production of H2O2 at an air-diffusion cathode, triggering the formation of OH from Fenton’s reaction with added Fe2+ catalyst. These radicals, in combination with those formed at a powerful boron-doped diamond (BDD) anode in an undivided cell, are used to degrade a mixture of model pesticides. The capability of the plant to produce H2O2 on site was initially optimized using an experimental design based on central composite design (CCD) coupled with response surface methodology (RSM). This aimed to evaluate the effect of key process parameters like current density (j) and solution pH. The influence of electrolyte concentration as well as liquid and air flow rates on H2O2 electrogeneration and current efficiency at optimized j and pH was also assessed. The best operation conditions resulted in H2O2 mass production rate of 64.9 mg min−1, 89.3% of current efficiency and 0.4 kWh m-3 of energy consumption at short electrolysis time. Performance tests at optimum conditions were carried out with 75 L of a mixture of pesticides (pyrimethanil and methomyl) as a first step towards the elimination of organic contaminants by solar photoelectro-Fenton (SPEF) process. The combined action of homogeneous (OH) and heterogeneous (BDD(OH)) catalysis along with photocatalysis (UV photons collected at a solar CPC photoreactor) allowed the removal of more than 50% of both pesticides in 5 min, confirming the fast regeneration of Fe2+ catalyst through cathodic reduction and photo-Fenton reaction.

Novel synthesis of N-doped porous carbons from collagen for electrocatalytic production of H2O2

Highly porous N-doped carbons for the electrocatalytic production of H2O2 via oxygen reduction were synthesized from paraformaldehyde cross-linked collagen through heating in vacuum at different temperatures (400–800°C). SEM images and N2 adsorption/desorption isotherms of such collagen-derived carbons reveal the formation of a sheet-like porous structure with increasing the carbonization temperature. A higher carbonization temperature favors the formation of a quaternary-N structure and the removal of oxygen-containing functional groups and therefore enhances the graphitic crystallinity, which were confirmed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The collagen-derived carbon synthesized at 800°C for 6h shows a good electrocatalytic activity for the four-electron oxygen reduction reaction (ORR). On the other hand, the carbons prepared at 400–800°C for 4h possess a high selectivity for the H2O2 production at potentials more negative than 0.6V. The H2O2 production percentage for the carbon synthesized at 400°C even reached 93%. In comparison with undoped carbons, the much more positive onset potentials and the nearly two-electron process of the ORR on these collagen-derived porous carbons reveal their unique electrocatalytic activity for H2O2 production.