Home Chemistry Electro-assisted methane oxidation to formic acid by way of in-situ cathodically generated H2O2 beneath ambient circumstances

Electro-assisted methane oxidation to formic acid by way of in-situ cathodically generated H2O2 beneath ambient circumstances

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Electro-assisted methane oxidation to formic acid by way of in-situ cathodically generated H2O2 beneath ambient circumstances

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Acid handled ketjen black (a-KB) preparation

Ketjen black (EC-600JD) (KB) powder (1 g) was added to 250 mL of 60% HNO3 (Samchun Chemical compounds) then the combination was stirred at 80 °C in an oil bathtub for 12 h. After acid-treatment, acid handled ketjen black (a-KB) was vacuum-filtered and washed with copious quantity of deionized (DI) water and dried in vacuum oven in a single day. Lastly, 800 mg of a-KB powder was obtained.

Characterization

The XPS spectra had been acquired utilizing a Nexsa (ThermoFisher Scientific) instrument with a Microfocus monochromatic Al-Kα X-ray supply. The HR-TEM was carried out on a JEM-F200 (JEOL) electron microscope with 200 kV acceleration voltage. EDS mapping had been analyzed by JEOL Twin SDD system with 200 kV. The ICP-OES was measured by iCAP 7000 (Thermo Scientific) to research the presence of Pt steel impurities within the catalyst and electrolytes.

Electrochemical ORR check

The electrochemical ORR check was carried out utilizing an electrochemical workstation (CHI760E, CH Devices) at room temperature (25 °C) beneath atmospheric stress. For the rotating ring disk electrode (RRDE) measurements, a three-electrode system was constructed with an RRDE (Pine analysis, E7R9 RRDE) (glassy carbon (GC) disk (0.2475 cm2) + Pt ring (0.1866 cm2)), a Ag/AgCl (saved in 3 M KCl, BASi) reference electrode, and a Pt foil counter electrode. The catalyst ink had been ready by dispersing the a-KB powder in resolution (Ethanol (C2H5OH, Sigma-Aldrich, 99.5%):DI = 3.5:1) with 5 wt% Nafion (Sigma-Aldrich) to attain focus of ~0.01 mg μl−1. After sonication for 30 min, 8 μl of the catalyst ink was drop casted onto a disk electrode and dried at room temperature. Cyclic voltammetry (CV) was carried out between 0.05 and 1.20 V (vs. RHE) in N2 (99.999%)-saturated 0.05 M H2SO4 (Sigma-Aldrich, 99.999%) and 0.1 M KOH (Sigma-Aldrich, 90%) at a scan price of 100 mV s−1 for 10 cycles, through which regular CV response was obtained. O2 (99.999%) fuel was equipped into the electrolyte for five min. The impedance spectroscopy was performed at 0.68 V (vs. RHE) from 100,000 to 1 Hz to find out the uncompensated resistance (Ru) in a high-frequency vary for iR-correction. The H2O2 manufacturing exercise was assessed by linear sweep voltammetry (LSV) from 1.1 to 0.2 V (vs. RHE) in O2-saturated 0.05 M H2SO4 and 0.1 M KOH at a scan price of 5 mV s−1 and rotating velocity of 1600 rpm. In the course of the LSV, the Pt ring potential was held at 1.23 V (vs. RHE). The H2O2 selectivity was calculated utilizing the next relation:

$${{{{{{rm{H}}}}}}}_{2}{{{{{{rm{O}}}}}}}_{2};{{{{{rm{Selectivity}}}}}},(%)=200times frac{{i}_{r}/N}{{i}_{d}+{i}_{r}/N}$$

(4)

the place ir, N, and id denote the ring present, assortment effectivity (37%), and disk present, respectively.

The Faradaic effectivity of H2O2 was calculated by equation under:

$${F.},{E.}_{{H}_{2}{O}_{2}}(%)=100times frac{{i}_{r}/N}{{i}_{d}}$$

(5)

The gathering effectivity (N) was decided utilizing the [Fe(CN)6]3-/4- redox system. Chronoamperometry was carried out at −0.3 V (vs. Ag/AgCl) whereas the ring potential was fastened at 0.5 V (vs. Ag/AgCl) for 60 s on the catalyst-deposited RRDE in N2-saturated 0.1 M KOH + 2 mM Okay3[Fe(CN)6] (Sigma-Aldrich, ≥99.0%). The background present was obtained equally, however the disk potential was 0.5 V (vs. Ag/AgCl). The gathering effectivity was calculated as follows:

$$N=frac{|{i}_{r}-{i}_{r,{bg}}|}{{i}_{d}}$$

(6)

The place ir, ir,bg, and id denote the ring present, background ring present, and disk present, respectively. The gathering effectivity was 37% (Supplementary Fig. 24).

Working electrode preparation

5 mg of a-KB catalyst was combined with 1 mL of 2-propanol (IPA, Sigma Aldrich, 99.5%) and 50 μL of 5 wt% Nafion. Then the combination was sonicated for 10 min. The catalyst ink was sprayed on the carbon paper (TGP-H-120 20percentWP, Toray) (11.25 cm2). The mass loading of a-KB on the carbon paper was 1 mg cm−2.

EMPO experiment

The EMPO experiment was performed in an H-type cell separated by Nafion 117 membrane utilizing a potentiostat (Ivium Vertex, Ivium Applied sciences). A 3-electrode system consisting of an a-KB sprayed carbon paper because the working electrode, Ag/AgCl (saved in 3 M KCl) reference electrode, and a Pt plate as a counter electrode was constructed. The working electrode was used with out pre-activation course of. The 0.05 M H2SO4 was used as an electrolyte (55 mL for each catholyte and anolyte). Catholyte was purged with O2 and CH4 (99.999%) gases for at the least 30 min previous to response and continuously purged at a circulate price of 100 sccm in the course of the response (0 V vs. RHE). The catholyte was repeatedly stirred at 700 rpm. Response temperature was maintained at 25 °C by water bathtub.

For the management experiment, all response circumstances had been the identical aside from feeding Ar fuel (99.999%) as an alternative of CH4.

For the 13CH4 (Icon Isotopes, 99.8%) isotope experiment, all response circumstances had been the identical aside from feeding 13CH4 as an alternative of 12CH4.

For the carbon-free ORR catalyst experiment, Au foil (Dasom RMS, 99.99%, 11.25 cm2) was utilized for working electrode whereas all different response circumstances had been the identical. The Au foil was used with out pre-activation course of.

For the time dependent manufacturing price evaluation, potential (0 V vs. RHE) was utilized for 1 h and 500 μL of electrolyte was extracted for every 5, 10, 15, 20, 25, 30, and 60 min. Different response circumstances had been the identical.

For the circulate price experiments, the circulate charges of CH4 and O2 had been diversified from 25 sccm to 200 sccm whereas all different response circumstances had been maintained.

For the potential dependent manufacturing price evaluation, utilized potential was diversified from −0.2 to +0.2 V (vs. RHE) for 30 min. Different response circumstances had been the identical.

For the identification of O supply experiment, Ar was purged as an alternative of O2. Different response circumstances had been the identical.

For the EPR experiment, 1 mmol of DMPO (Sigma-Aldrich, ≥98%) was utilized as a spin entice earlier than the response. Different response circumstances had been the identical aside from feeding O2 or O2 + CH4 gases.

For the trapping experiments, 400 and 40 μmol of TBA (Sigma-Aldrich, ≥99.5%) and BQ (Sigma-Aldrich, ≥98%) had been added earlier than the response as ∙OH and ∙OOH radical scavengers, respectively. Different response circumstances had been the identical.

For the chronoamperometry experiment, O2 + Ar and O2 + CH4 (100 sccm every) had been purged alternatively each 10 min for 1 h. Different response circumstances had been the identical.

For the CH3OH (Sigma-Aldrich, ≥99.9%) oxidation experiment, all response circumstances had been the identical aside from injecting 100 μmol of CH3OH earlier than the response as an alternative of CH4.

For the alkaline EMPO experiment, all response circumstances had been the identical aside from making use of 0.1 M KOH as an electrolyte as an alternative of 0.05 M H2SO4.

For the electro-assisted C2H6 partial oxidation experiment, all response circumstances had been the identical besides feeding C2H6 as an alternative of CH4.

For the soundness check, the electrolyte-flowing H-cell setup was established. 550 mL of 0.05 M H2SO4 was circulated by 10 mL min−1. The EMPO response was carried out for six h. Different response circumstances had been the identical.

Methane partial oxidation utilizing business H2O2

CH4 partial oxidation utilizing business H2O2 (30 wt% in H2O, Sigma-Aldrich) was performed utilizing cathode a part of H-type cell. 55 mL of 0.05 M H2SO4 was crammed in cathode half and the answer was purged with Ar and CH4 at 100 sccm concurrently. Ar was purged as an alternative of O2 to maintain stability of partial circulate of CH4. Industrial H2O2 was injected throughout response time (30 min) by way of syringe pump. The quantity of H2O2 equipped was decided primarily based on RRDE evaluation.

$${The; quantity; of},{{H}}_{2}{O}_{2}=frac{{F.E.}_{{H}_{2}{O}_{2}}occasions jtimes Atimes t}{ntimes F}$$

(7)

the place, F.E.H2O2 = 81.8%, j is present density, A is space of electrode, t is response time, n is moles of electron to supply 1 mole of H2O2, and F is faraday fixed. The answer was stirred at 700 rpm and stored at 25, 50, 70, or 90 °C by water bathtub.

Methanol oxidation utilizing business H2O2

CH3OH oxidation utilizing business H2O2 was performed utilizing cathode a part of H-type cell. 55 mL of 0.05 M H2SO4 was crammed in cathode half and 100 μmol of CH3OH was injected earlier than the response. Industrial H2O2 was fed throughout response time (30 min) by way of syringe pump. The quantity of equipped H2O2 was decided primarily based on RRDE evaluation.

1H-NMR evaluation of liquid merchandise

The focus of the liquid merchandise was quantified by 1H-NMR (Agilent 600 MHz). Sometimes, 430 μL pattern was combined with 50 μL of D2O, and 20 μL of 6 mM dimethyl sulfoxide (DMSO, Sigma-Aldrich, 99.9%) was added as an inner commonplace.

13C-NMR evaluation of liquid merchandise

Because of the decrease detection restrict of 13C-NMR than that of 1H-NMR, freeze-drying previous to evaluation to fight low concentrations, steadily <100 μM C, was performed55. 5 mL of 1 M KOH was combined with 50 mL of pattern to alkalify formic acid to formate anion to forestall sublimation throughout freeze-drying. Then pattern was frozen by liquid nitrogen. Frozen pattern was lyophilized at −80 °C at 200 mtorr till dry (48 h) (CH3OH and CH3OOH was sublimated on this step). Freeze-dried pattern was re-dissolved in 1 mL DI water. 500 μL of re-dissolved pattern was certified by 13C-NMR (Agilent 600 MHz).

GC evaluation of fuel merchandise

The fuel merchandise from the EMPO response had been quantified by on-line fuel chromatography (GC, Agilent 6890). A flame ionization detector was used to detect CO and CO2. A methanizer was utilized to extend the detection sensitivity of CO and CO2. The GC system was geared up with a ShinCarbon ST column (Restek) to separate fuel merchandise. The calibration of the GC was carried out by flowing three calibration fuel mixtures with CO- and CO2-concentrations starting from 10 to 100 ppm (Supplementary Fig. 25).

EPR experiment

The EPR spectrum of electrolytes was measured at KBSI Seoul Western Middle utilizing CW/Pulse EPR system with the next parameters: frequency 9.852 GHz; energy 3 mW; modulation frequency 100 kHz; modulation amplitude 1 G; time fixed 20.48 ms; conversion time 20.00 ms; scan 8; room temperature.

Synthesis of CH3OOH

The CH3OOH was synthesized by the modified procedures from the previously-reported technique56. On the three-neck flask, 62.5 g of H2O, 37.5 g of 30% H2O2, and 25 g of dimethyl sulfate ((CH3O)2SO2, Sigma-Aldrich, ≥99.5%) had been combined. Subsequently, 52.5 g of 40 wt% KOH aqueous resolution was added dropwise very slowly into the answer with stirring to induce a nucleophilic substitution response. The general response is exothermic. Then, the gas-phase merchandise had been generated by the warmth of the response. The generated gas-phase merchandise had been collected as a liquid section within the vial by the condensation. Diluting the concentrated CH3OOH within the DI water, electrochemical evaluation was carried out. The synthesized CH3OOH was confirmed and quantified by 1H-NMR evaluation (Supplementary Fig. 26).

Discount response check of CH3OOH, CH3OH, and HCOOH

The reducibility check of CH3OOH, CH3OH, and HCOOH (Sigma-Aldrich, ≥98%) had been additionally carried out in the same electrochemical configurations as talked about above. A working electrode ready by spraying a-KB primarily based catalyst ink on carbon paper (11.25 cm2) was used. The mass loading of a-KB on the carbon paper was 1 mg cm−2. Earlier than the check, CV was carried out for the electrochemical cleansing of the electrode floor between 0.05 and 1.2 V (vs. RHE) at a scan price of 100 mV s−1 for 20 cycles in N2-saturated 0.05 M H2SO4. LSV was then carried out from 1.1 to 0.1 V (vs. RHE) at a scan price of 10 mV s−1 in N2-saturated 0.05 M H2SO4 containing 0, 10, 20, and 40 mM of CH3OOH, CH3OH, and HCOOH, respectively.

Calculation of Gibbs free power and commonplace potential

Customary Gibbs free energies of chosen coupled reactions and their corresponding commonplace cell potentials have been calculated by Eqs. (8, 9) primarily based on thermodynamic information (Supplementary Desk. 3)57

$$triangle G=triangle H-Ttriangle S$$

(8)

$$E=frac{-triangle G}{{nF}}$$

(9)

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