CO2 electroreduction to multicarbon merchandise in strongly acidic electrolyte through synergistically modulating the native microenvironment

Characterizations

The morphology and construction of ER-CuNS and F-CuNS had been investigated utilizing transmission electron microscopy (JEOL JEM-2100Plus) and the high-angle annular dark-field scanning transmission electron microscopy with a spherical aberration corrector (HAADF-STEM, Thermo scientific Themis Z 3.2). The crystalline phases of all samples had been evaluated by X-ray diffraction (XRD, Rigaku Miniflex-600) with a Cu Kα radiation (λ = 0.15406 nm, 40 kV). X-ray photoelectron spectroscopy (XPS) spectrum was collected by utilizing a Thermo Scientific Ok-Alpha spectrometer outfitted with an Al Kα (hv = 1486.6 eV) excitation supply.

Synthesis of electrochemically decreased Cu nanosheet (ER-CuNS)

Sometimes, 10 mL of 6 M NaOH aqueous answer was added dropwise to 10 mL of 100 mM CuCl₂ aqueous answer below magnetic stirring (1000 rpm). The combination was saved stirring at room temperature for 30 min. After that, the combination was transferred right into a Teflon-lined autoclave, capped, and heated at 100 °C for 12 h. After cooling all the way down to room temperature, the ensuing product was collected by centrifugation. The product was washed a number of instances with ultrapure water in addition to ethanol, after which dried in a vacuum oven at 50 °C in a single day. Subsequently, the ER-CuNS true catalyst was obtained through in situ electrochemical discount from CuO NS loaded on gas-diffusion-electrode (GDE) embedded inside stream cell electrolyzer (element see part “Preparation of working electrode” under).

Synthesis of flat Cu nanosheet (F-CuNS)

The F-CuNS had been synthesized in line with a reported methodology⁵³. Sometimes, Cu(NO₃)₂·3H₂O (50 mg) and L-ascorbic acid (100 mg) had been blended with 15 mL of ultrapure water, and the combination was saved stirring at room temperature for 30 min to type a homogeneous answer. Then hexadecyl trimethyl ammonium bromide (100 mg) and hexamethylenetetramine (100 mg) had been added adopted by 30 min of stirring. The combination answer was purged with N₂ for 15 min to take away the trapped O₂. After that, the vial was transferred into an oil bathtub set to 80 °C. The response was continued below magnetic stirring for 3 h. The ensuing product was collected by centrifugation. The product was washed a number of instances with ultrapure water in addition to ethanol, and at last dispersed in ethanol to be used.

Preparation of working electrode

(1) ER-CuNS electrode. Sometimes, 14 mg of CuO NS and seven mL of ethanol had been blended by sonicating for 60 min, and 30 μL of Nafion answer was added, adopted by sonicating for an additional 60 min to acquire a homogeneous catalyst ink. The catalyst ink was then sprayed on hydrophobic porous polytetrafluoroethylene GDE (2 cm × 2 cm). The GDE earlier than and after loading catalysts was weighed to find out the loading quantity of the catalyst (1.7 mg cm⁻²). The ER-CuNS electrode was obtained through in situ electrochemical discount from CuO NS electrode below galvanostatic mode for 60 min in 0.1 M Ok₂SO₄, with fixed present density at 20 mA cm⁻². (2) F-CuNS electrode. The 14 mg as-prepared F-CuNS pattern was dispersed in 7 mL ethanol and ultrasonicated for 60 min. Later, 30 μL of Nafion answer was added, adopted by sonicating for an additional 60 min to acquire a homogeneous catalyst ink. The catalyst ink was sprayed on hydrophobic GDE, with a loading quantity of F-CuNS catalyst at 1.7 mg cm⁻² as effectively.

Preparation of IrO_x/Ti-mesh anode

The IrO_x/Ti-mesh anode was ready through a dip coating and thermal deposition methodology⁵⁴. Sometimes, Ti-mesh was first washed with ultrapure water and acetone, after which etched for 45 min in 6 M HCl at 80–90 °C. After that, the dip coating answer was obtained by dissolving 30 mg IrCl₃·xH₂O into 10 mL isopropanol with 10 v% HCl. Subsequently, the etched Ti-mesh was dipped into the dip coating answer, then dried for 10 min at 100 °C within the oven and underwent calcination at 500 °C for 10 min in a muffle furnace below air environment. The dipping and calcination process was repeated for a number of instances till the IrO_x loading reached about 2 mg cm⁻². Lastly, the ensuing IrO_x/Ti-mesh anode was used for subsequent electrochemical acidic CO₂RR measurements.

Electrochemical measurements

The acidic CO₂RR efficiency was evaluated in a three-electrode system in a stream cell meeting (Supplementary Fig. 2). The used stream cell meeting consists of fuel stream chamber, anolyte chamber, and catholyte chamber. Every chamber contained an inlet and outlet for fuel or electrolyte. The window of the electrode uncovered was a sq. with an space of 0.5 cm². The anolyte chamber was separated from the catholyte chamber by a Nafion 117 cation trade membrane (DuPont). 25 mL of 0.05 M H₂SO₄ containing varied contents of KCl (0/0.1/0.5/3 M, comparable to electrolyte pH of 0.97/0.90/0.83/0.51) was used as catholyte, and 25 mL of 0.05 M H₂SO₄ aqueous answer was used as anolyte. The electrolyte in cathode and anode had been circulated by a peristaltic pump. In the course of the measurements, high-purity CO₂ (99.999%) fuel was constantly equipped to the fuel chamber at a charge of fifty sccm (or 2/5/10/15/20/30 sccm). The as-obtained ER-CuNS electrode or F-CuNS electrode was utilized because the working electrode. The Ag/AgCl (3.5 M KCl) and IrO_x/Ti-mesh had been employed because the reference electrode and counter electrode, respectively. All potentials had been measured in opposition to an Ag/AgCl reference electrode, and transformed to the reversible hydrogen electrode (RHE) reference scale through Nernst operate with iR compensation as under:

All of the electrochemical checks had been performed in a three-electrode system utilizing a DH7001A electrochemical workstation (Donghua Testing Know-how Co., Ltd.), at room temperature. The electrochemical impedance spectroscopy (EIS) examine was investigated by making use of an open circuit voltage in a frequency vary from 100 kHz to 0.1 Hz with an amplitude of 5 mV (Supplementary Figs. 11–12, Supplementary Desk 1). The linear sweep voltammetry (LSV) experiments had been scanned in acidic electrolyte with the scan charge of fifty mV s⁻¹. Electrochemical lively floor space (ECSA) of ER-CuNS and F-CuNS was decided by scanning cyclic voltammetry (CV) curves at non-faradaic area (0.05–0.07 V_RHE) at various scan charges (1–15 mV s⁻¹). The OH⁻ adsorption curves of ER-CuNS and F-CuNS had been examined by way of CV methodology at a scan charge of fifty mV s⁻¹ in 1 M KOH³³. Acidic CO₂RR measurements had been performed below potentiostatic mannequin, whereas fuel merchandise and liquid merchandise had been decided severally. The soundness measurements of CO₂RR below acid media had been carried out at potentiostatic situations (−1.45 V_RHE) to file the present density and FE of ER-CuNS in 0.05 M H₂SO₄ and three M KCl catholyte inside 30 h.

CO₂RR product evaluation

Until in any other case said, CO₂ fuel was led into fuel chamber of stream cell at ambient stress and room temperature, after which injected right into a fuel chromatograph (GC, Panna A60) after CO₂RR to investigate fuel merchandise. The GC was outfitted with a thermal conductivity detector (TCD) for analyzing H₂, and a flame ionization detector (FID) for analyzing carbonaceous substances, whereas calibrated by utilizing commonplace fuel (Dalian particular gases CO., LTD) earlier than measurements. Every quantitative sampling was carried out 3 times to realize correct outcomes. The FE of fuel merchandise was calculated as follows:

the place N is the variety of transferred electron for focused merchandise, Faraday fixed F = 96,485 C mol⁻¹, v is the fuel stream charge measured by a stream meter, c is the quantity focus of fuel merchandise (CO, CH₄, C₂H₄, or H₂) from the GC knowledge, stress P = 1.01 × 10⁵Pa, fuel fixed R = 8.314 J mol⁻¹ Ok⁻¹, temperature T = 298.15 Ok, J means the full recorded present.

Then again, liquid merchandise had been diluted and analyzed by ¹H NMR (Bruker AVANCE III HD 400 MHz) with water peak suppression, through which 100 μL of the catholyte was ready with 10 μL dimethyl sulfoxide (DMSO, 1200 ppm, the inner commonplace answer), 90 μL D₂O and 400 μL H₂O. The concentrations of liquid merchandise had been elucidated by its NMR peak space relative to the inner commonplace. FE of liquid merchandise was decided as under:

the place n is the moles of liquid product within the cathodic compartment, N is the electron switch quantity, F = 96,485 C mol⁻¹, t is the response time, J is the recorded present. The partial present density below completely different utilized potentials was decided by multiplying corresponding FE of every part and the full geometric present density. Be aware that for each set of knowledge, three particular person repeated measurements utilizing the identical batch of ready electrodes had been performed to acquire the common FE and present density values with corresponding error bars (commonplace deviations).

The SPCE of CO₂ in the direction of producing C₂₊ was calculated as follows at 25 °C, 1 atm:

the place j means the partial present density of C₂₊, N stands for electron switch²¹. Be aware that for exactly analyzing fuel merchandise and figuring out SPCE at very low CO₂ fuel stream charge (2 sccm), the GC commonplace curve was re-calibrated by utilizing commonplace fuel with increased focus (tens of hundreds ppm), and CO₂RR operation time was prolonged to 4 h to let the system completely enter the regular state earlier than gathering knowledge.

Hydrogen evolution response (HER) take a look at

HER take a look at was carried out with a CHI660E workstation by utilizing a three-electrode setup in a single cell, to judge the HER efficiency of ER-CuNS in numerous electrolytes (0.05 M H₂SO₄ with 0/0.5/1/2/3 M KCl aqueous answer). Glassy carbon rotating disk electrode (GC-RDE, 0.196 cm²) loaded with catalyst was used because the working electrode. The carbon rod and Ag/AgCl (3.5 M KCl) electrode had been used because the counter electrode and reference electrode, respectively. Earlier than measurements, the electrolytes had been saturated by N₂ for 10 min to take away O₂ purity. LSV measurements had been carried out with a scan charge of 10 mV s⁻¹ at completely different rotation velocity.

Measurement of electric-field-induced enrichment of Ok⁺

Electrical-field-induced Ok⁺ enrichment was measured in an electrolyte much like the catholyte for acidic CO₂RR. The electrode loaded with ER-CuNS or F-CuNS was first performed in 0.05 M H₂SO₄ aqueous answer with 3 M KCl components at −1.45 V_RHE (with out iR compensation). After working for 120 s, the electrode was instantly raised above the electrolyte and transferred into 5 mL pure water, throughout which the voltage was saved. After immersing in water, the voltage was eliminated to launch any adsorbed Ok⁺ from the electrode³⁷. The transferred electrodes from the identical aqueous answer with out making use of voltage had been used because the clean background. Subsequently, the quantity of Ok⁺ within the water was decided utilizing an inductively coupled plasma optical emission spectrometer (ICP-OES, Atom scan Benefit, Thermo Jarrell Ash, USA). Lastly, the quantity of Ok⁺ in ultrapure water with the background deducted represents the true quantity of Ok⁺ adsorbed on the floor of the ER-CuNS or F-CuNS catalysts. The obtained outcomes had been normalized by ECSA for comparability.

In situ attenuated whole reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS)

ATR-SEIRAS was carried out on a Nicolet iS50 FT-IR spectrometer outfitted with an MCT detector cooled with liquid nitrogen. The Au-coated Si semi-cylindrical prism (20 mm in diameter) was used because the conductive substrate for catalysts and the IR reflection factor. The catalysts suspensions had been dropped on the Au/Si floor because the working electrode. The mass loading of the catalyst was 1 mg/cm⁻² and the electrolyte was 0.05 M H₂SO₄ with/with out 3 M KCl components. In situ ATR-IR spectra had been recorded through the stepping of the working electrode potential.

In situ Raman spectroscopy

To find out the native pH on the electrode floor below CO₂RR working situations, in situ Raman spectra had been acquired utilizing a confocal Raman microscope (WITec Alpha 300R). The excitation supply was a 633 nm laser with the ability of three mW and grating of 600 grooves/mm, and a 50× goal (Zeiss LD EC Epiplan-Neofluar Dic) was used. Every spectrum was obtained with an acquisition time of 10 s and three instances of accumulation. The electrochemical reactor for in situ Raman measurements was a C031-4 CO₂RR stream cell bought from Wuhan Gaoshi Ruilian Know-how Co., Ltd, and ER-CuNS or F-CuNS catalyst was loaded on the carbon paper GDE and built-in into the stream cell. Particulars to calculate the native pH primarily based on the Raman sign of HCO₃⁻ and CO₃²⁻ ions on the electrode floor will be present in Supplementary Data Be aware S1.

DFT calculations

On this work, all calculations are carried out inside the Perdew-Burke-Ernzerhof generalized gradient approximation (GGA)⁵⁵ with D3 kind van der Waals interplay (vdW) correction^56,57 applied in Vienna ab initio simulation bundle (VASP)⁵⁸. The projector augmented wave (PAW) potential⁵⁹ and the plane-wave cut-off power of 450 eV are used. Our calculations have used a slab mannequin composed of 4 layers of 4 × 3 × 3 representing the Cu (111) surfaces separated by 15 Å of vacuum area. The slabs and adsorbate configurations on this work embody a single layer of H₂O with and with no Ok⁺. Adsorbates and the highest two layers of the slab had been geometrically relaxed for every binding website, and essentially the most secure adsorbate configuration was used to find out the digital part of the free power. The three × 3 × 1 Monk-horst k-point meshes had been used for the Brillouin-zone integrations of supercell fashions. The standards of convergence had been set to 1 × 10⁻⁵eV for the self-consistent discipline (SCF) and 0.02 eV/Å for ion steps. We additionally employed the climbing picture nudged elastic band methodology to find out the transition state for CO coupling on the Cu (111) surfaces⁶⁰. Furthermore, the power convergence tolerance on every atom was set to be 0.05 eV/Å.

COMSOL multiphysics simulations

The electrical discipline and Ok⁺ focus inside the neighborhood of Cu electrodes had been simulated by fixing the Poisson-Nernst-Planck equations utilizing the COMSOL Multiphysics finite-element-based solver (https://www.comsol.com/). The Nernst-Planck equations within the regular state used to resolve the ion focus distribution of answer species are given by:

the place c_i, D_i, and z_i are the focus, the diffusion coefficient (D₁ = 1.957 × 10⁻⁹ m²/s, D₂ = 9.311 × 10⁻⁹ m²/s, D₃ = 1.97 × 10⁻⁹ m²/s, and D₄ = 1.065 × 10⁻⁹ m²/s)⁶¹, and the cost valence (z₁ = z₂ = +1, z₃ = −1 and z₄ = −2) of species i (1 for Ok⁺, 2 for H⁺, 3 for Cl⁻, and 4 for SO₄²⁻), respectively. As well as, F, R, and T signify the Faraday fixed, fuel fixed, and absolute temperature (T = 293.15 Ok), respectively, and ψ is the electrostatic potential that satisfies the Poisson equation:

the place ε₀ is the permittivity of vacuum and ε_r is the relative permittivity of water (ε_r = 78). {The electrical} double layer (EDL) was modeled utilizing the Gouy-Chapman-Stern mannequin, which consists of a Helmholtz layer and a diffusion layer. The thickness of the Helmholtz layer was taken because the radius of a hydrated potassium ion (0.33 nm)⁶². The diffusion layer was established as the results of a dynamic equilibrium between electrostatic forces and diffusion. The so-called outer-Helmholtz aircraft (OHP) separates the EDL on the electrolyte facet from the Helmholtz layer towards the majority electrode facet. Two three-dimensional fashions of 300 × 200 × 20 nm³ had been constructed to signify the native porous construction and the graceful floor of Cu electrodes in line with the TEM pictures, which had been thought-about to be immersed into the electrolyte field of 500 × 400 × 220 nm³, as proven in Fig. 3h–i. Within the system, the partial differential Eqs. (1)–(2) are solved below the next preliminary and boundary situations. The preliminary values of species concentrations with out utilized potential had been assumed to be identical within the bulk electrolyte (3 M KCl and 0.05 M H₂SO₄). In the meantime, Dirichlet boundary situations specify the focus of species and nil potential within the bulk. To make sure the accuracy of the theoretical mannequin, a small electrode potential of 0.05 V was utilized by way of all simulations. The electrical discipline worth and the potential worth on the OHP had been used as blended boundary situation for the equation:

Free tetrahedral meshes had been used for all simulations. Meshes had been set to be the densest on the floor of the electrodes, the place the factor dimension was 0.2 nm.