Cathodic Hydrogen Peroxide Electrosynthesis Using Anthraquinone Modified Carbon Nitride on Gas Diffusion Electrode

Abstract

Electrochemical synthesis of hydrogen peroxide from oxygen and water can be a cost-effective and energy-efficient alternative to the traditional approach which requires high energy input and expensive noble metal catalysts and has a large CO2 footprint. The availability of selective electrocatalysts and performance validation of a device represent current research needs toward this goal. Herein, we report an efficient electrocatalytic system for hydrogen peroxide production based on anthraquinone molecular catalysts which are tethered onto carbon nitride (C3N4) conductive supports. Anthraquinone enables highly selective synthesis of hydrogen peroxide via two-electron oxygen reduction. The optimal electrolyte pH was identified to both facilitate H2O2 electrochemical synthesis and minimize H2O2 decomposition. The anthraquinone-functionalized C3N4 supports were then adapted into a gas diffusion cathode configuration to greatly enhance the mass transport of oxygen reactants. The device fabricated in this study achieved an optimal H2O2 production rate of 60.1 mmol gcatalyst –1 h–1 at a maximum Faradaic efficiency of 42.2%.

Modular Hydrogen Peroxide Electrosynthesis Cell with Anthraquinone-Modified Polyaniline Electrocatalyst

“…An iridium oxide coated titanium mesh was used as the anode, where water was oxidized to protons and oxygen. The anode and cathode “sandwiched” a cation exchange membrane (Nafion 115) to inhibit the anodic oxidation and/or the self-decomposition of H 2 O 2 . A thin water channel (1.5 mm) was adopted to minimize charge transfer resistance between the two electrodes .…”

“…Over a wide range of total current (4 to 100 mA), the flow cell showed consistent and high selectivity of H 2 O 2 generation (>90%), for example, 1.80 mol g catalyst –1 hr –1 of H 2 O 2 production at 100 mA (25 mA cm –2 ) with 95.83% selectivity (Figure b). Compared with the AQ-PANI­(NS-CNT) electrode in an immersed electrode setup of the same current density (10 mA cm –2 ), the AQ-PANI­(NS-CNT) electrode in a flow cell setup showed both higher generation (0.68 mol g catalyst –1 hr –1 vs 0.21 mol g catalyst –1 hr –1 ) and a higher Faradaic efficiency (91.18 vs 56.75%) due to faster O 2 transport and reaction kinetics . The reactor exhibited a stable H 2 O 2 generation capability for 50 h (>90% Faradaic efficiency), with less than 0.3 V of a cell potential increase during the long-term operation (Figure d), which makes this electrochemical cell one of the most stable systems reported so far (Table S4).…”

“…To calibrate the peak area to the H 2 O 2 concentration, several H 2 O 2 standard solutions were used with the area of each resorufin peak detected at 560 nm at a retention time of 1.1 min. Faradaic efficiency (FE) was calculated by eq , where V is the volume of the electrolyte (L), C H 2 O 2 is the H 2 O 2 concentration in the electrolyte (mol L –1 ), n is the number of electrons transferred in oxygen reduction to hydrogen peroxide ( n = 2), N A is Avogadro’s number, q is total charge passed (Coulomb), and the constant 6.24 × 10 18 is the number of electrons in per Coulomb of charge (Coulomb –1 ) …”

“…Although a few materials have been previously reported as feasible electrocatalytic substrates for AQ and its derivatives, such as glassy carbon, 9 indium tin oxide, 10 graphene oxide, 11 and carbon nanotubes (Table S1), 12 the AQ coverage density on the surface is relatively low (0.04−0.43 nmol cm −2 ) due to the limited amount of anchoring sites in these materials for AQ attachment. The recently reported carbon nitride (C 3 N 4 ), covalently decorated with AQ, greatly improved the coverage density with its amine groups at edge sites of its nanosheet, 13 while the low conductivities of the C 3 N 4 substrate restricted the overall performance of the composite material. Therefore, a conductive substrate with plentiful end groups is preferred as a supporting matrix.…”

Probing Oxygen-to-Hydrogen Peroxide Electro-Conversion at Electrocatalysts Derived from Polyaniline

“…Its industrial production largely depends on the anthraquinone process, an energy-intensive process that involves the hydrogenation of 2-alkylanthraquinone using expensive palladium catalysts and generates numerous by-products [ 1 , 2 ]. Indeed, to address the high and increasing demand (application for disinfection, textile bleaching, wastewater treatment and renewable energy storage), the four possible methods to produce H 2 O 2 include the traditional anthraquinone process, direct synthesis, photocatalysis and electrocatalysis [ 3 , 4 , 5 ]. As an alternative to the anthraquinone process, the direct reaction (H 2 + O 2 → H 2 O 2 ) is conceptually the simplest method, but it requires high pressure and finding H 2 that is not yet produced in a decarbonized way.…”