Preparation of CuO nanopowders

CuO nanopowders have been fabricated by a solvothermal methodology. Copper chloride dehydrate (1.02 g, 6.0 mmol) and 50 mg Nano-carbon black have been first dissolved in 30 ml 2 M sodium hydroxide answer, below stirring for 30 min at room temperature. Then the combination was transferred right into a Teflon-lined stainless-steel autoclave (50 mL) for solvothermal remedy at 130 °C for 12 h, and subsequently centrifuged thrice with deionized water and ethanol, respectively. The pattern was lastly dried in a vacuum oven at 80 °C for six h.

Preparation of fuel diffusion electrodes (GDEs)

As for GDE with the Pb-Cu pre-catalyst, a catalyst slurry of 15 mg CuO nanopowders, 3 mg Pb(NO₃)₂, 1 mL methanol and 50 μL of Nafion answer was combined and sonicated. Then, the slurry was drip-coating on a (2 cm × 2 cm) GDL, the as-prepared GDL was annealed in a tube furnace below 200 °C for two h. As for Pb-Cu-l and Pb-Cu-h, to control the Pb focus, we adjusted the quantity of the Pb salts in pre-catalyst inks to 1 mg and 6 mg, respectively. Electrodes with the Cu pre-catalyst have been ready by an identical process, 15 mg CuO nanopowders, 1 mL methanol and 50 μL of Nafion answer was combined to type a catalyst slurry and sonicated. The following procedures for the preparation have been the identical as these for the preparation of GDE with the Pb-Cu pre-catalyst.

The as-prepared GDEs have been run for 300 s at −0.38 V (vs. RHE) in 1 M KOH, till a secure present has been gained to verify the pre-catalysts have been utterly electro-reduced to a secure state because the CORR catalysts.

The electrode potentials have been rescaled to the RHE reference by the next equation:

Structural characterization

The morphologies of those catalysts have been acquired utilizing a Hitachi FE-SEM S-4800 SEM operated at 1.0 kV. Excessive-resolution transmission electron microscopy (HRTEM) pictures have been taken on a JEOL JEM-2100F TEM operated at 200 kV. Scanning transmission electron microscopy (STEM) was carried out on FEI Titan Cubed 60–300 at an accelerating voltage of 300 kV and JEOL ARM-200F geared up with a chilly area emission gun and a Cs corrector (CEOS) for probing lenses on the operation voltage of 200 kV. Excessive-resolution EDX was based mostly on super-X detector. XPS measurements have been carried out on PHI 5700 ESCA System utilizing Al Kα X-ray radiation (1486.6 eV) for excitation. Powder XRD patterns have been obtained with a MiniFlex600 instrument in Bragg-Brettano mode utilizing 0.02° divergence with a scan charge of 0.1° s⁻¹.

Operando X-ray absorption positive spectroscopy (XAFS)

The operando Cu Okay-edge XAFS measurements have been carried out on the 1W1B beamline of the Beijing Synchrotron Radiation Facility, China. The Cu Okay-edge fast X-ray absorption positive construction (QXAFS) information have been recorded from 8.8 to 9.2 keV in fluorescence mode with a step dimension of 0.5 eV on the close to edge. About 40 s have been consumed for every QXAFS spectrum (together with 30 s to gather the information and 10 s to reset the detector place).

The Pb-Cu GDE (similar because the electrochemical measurements) was carried out with a chronoamperometry course of at −0.68 V (vs. RHE) in a home-made flow-cell kind reactor for the operando XAS measurements, much like the movement cell used for desire measurements, and the one distinction is that the outer floor of the fuel chamber was changed with the Kapton tape (Supplementary Fig. 8). Within the movement cell reactor, Hg/HgO reference electrode (1 M KOH), Fe-S/ Ni foam electrode and anion trade membrane (Fumatech FAB-PK-130) have been used because the reference electrode, anode, and membrane, respectively. 1 M KOH aqueous answer was used because the electrolyte and CO (Air France, 99.99%) was constantly equipped to the fuel chamber throughout CORR. XAS information have been processed utilizing Athena and Artemis software program included in a normal IFEFFIT package deal. As reference samples, ex-situ Cu Okay-edge XAFS information of business Cu NPs and CuO powders was carried out. These energy samples have been ready by uniformly putting powders on a bit of three M tape.

Operando attenuated complete reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS)

ATR-SEIRAS measurements have been carried out with a Nicolet iS50 infrared spectrophotometer with a built-in mercury cadmium telluride (MCT) detector. Completely different Cu-based catalysts coated on the Au/Si substrate was used because the working electrode, a Hg/HgO electrode and a graphite rod have been utilized because the reference and counter electrodes (Supplementary Fig. 16), respectively.

Au/Si substrate was ready as follows: the hemicylindrical Si prism was bought from IRUBIS GmbH. The Au movie on the reflecting aircraft of Si prism (Au/Si substrate) was ready based on the so-called ‘two-step moist course of’. Firstly, the reflecting aircraft of Si prism was mechanically polished with 1.0 µm, 0.3 µm and 0.05 µm Al₂O₃ powder, sonicated in acetone and water respectively, soaked in piranha answer and completely rinsed with Milli-Q water (18.2 MΩ·cm). Then the whole reflecting aircraft was immersed in a 40% NH₄F answer for 1.5 min to terminate the Si floor with hydrogen, and was immersed within the plating answer containing 0.015 M HAuCl₄, 0.15 M Na₂SO₃, 0.05 M Na₂S₂O₃, and 0.05 M NH₄Cl at 60 °C for 3 min to deposit Au movie.

The ATR-SEIRAS spectra have been acquired at a decision of 4 cm⁻¹ with unpolarized IR radiation at an incidence angle of ca. 70°. The electrolyte was 0.1 M KOH, which was saturated with CO or purged with Ar fuel in the course of the experiment. The electrode potential was held at an open circuit potential (OCP) and a background spectrum was recorded. The entire spectra are proven within the absorbance unit as -log (I/I₀), the place I and I₀ signify the intensities of the mirrored radiation of the pattern and background spectrum, respectively. The electrode potential was altered from 0.05 to −0.80 V vs. RHE in a stepwise method. Concurrently, the infrared spectra have been recorded with a time decision of 30 s per spectrum at a spectral decision of 4 cm⁻¹.

The electrode potentials have been rescaled to the RHE reference by the next equation:

To make our mechanistic insights based mostly on ATR-SEIRAS extra convincing, the catalytic efficiency was additionally evaluated within the ATR-SEIRAS cell. We achieved a peak n-propanol FE of ~37% at −0.68 V (vs. RHE), ~2 occasions greater n-propanol selectivity than that of the Cu catalysts (17%). As well as, within the potential vary of −0.58 V to −0.78 V, the Pb-Cu catalysts confirmed a lot enhanced n-propanol selectivity in contrast with the Cu catalysts. Moreover, each of the n-propanol and ethylene FEs have been promoted and the ethanol was suppressed after the Pb doping, much like the efficiency obtained within the flow-cell reactor (Supplementary Fig. 50).

Operando surface-enhanced Raman spectroscopy (SERS)

The operando SERS measurements have been carried out utilizing a Horiba Scientific Xplora Raman Microscope in a modified movement cell and a water immersion goal (100×) with a 633 nm laser (NA = 1.0, WD = 2.0 mm; LUMPLFLN-60X/W; Olympus Inc.; Waltham, MA). Every spectrum was acquired utilizing a 5-s integration and an averaged 10 scans. The spectra have been recorded and processed utilizing the LabSpec 6.0 software program. The identical working electrode ready for the electrochemical efficiency testing was utilized for operando Raman evaluation. An Ag/AgCl electrode (3 M KCl) and a graphite rod have been used because the reference electrode and the counter electrode (Supplementary Fig. 19), respectively. A 1 M KOH aqueous answer was used because the electrolyte. CO fuel feedstocks have been constantly equipped to the fuel chamber in the course of the measurement.

The potentials in Raman measurements have been transformed to values close to RHE utilizing the equation:

The catalytic efficiency was additionally evaluated within the Raman cell. Within the potential vary from −0.58 to −0.78 V, the height n-propanol FE of ~43% was obtained at −0.68 V (vs. RHE) on the Pb-Cu catalysts, ~2 occasions greater n-propanol than that on the Cu catalysts. Apart from, each of the n-propanol and ethylene FEs have been promoted and the ethanol was suppressed after the Pb doping, much like the efficiency within the flow-cell reactor and ATR-SEIRS cell (Supplementary Fig. 51).

Temperature programed desorption (TPD)

The GDEs (similar because the electrochemical measurements) have been carried out with a chronoamperometry course of at −0.68 V (vs. RHE) and dried in a vacuum oven. Then, the samples (together with catalysts and GDLs) have been grinded into powder for CO desorption measurements. CO desorption measurement of grinded GDL with the identical parameter was additionally carried out to exclude the contribution of the GDL assist.

The CO adsorption examine was carried out utilizing temperature-programed desorption instrument geared up with a thermal conductive detector (AutoChem II 2920). The catalysts have been degassed below 100 °C with steady Ar movement to take away the adsorbed gases on catalysts floor. After 1 h degassed course of, the CO fuel was launched to permit enough adsorption of CO on the catalysts. The remainder CO was swept utilizing Ar. The temperature programed was began with steady Ar in fixed velocity to convey the desorbed CO to the detector.

Electrochemical measurements

With out specification, the CORR efficiency of assorted catalysts was measured at 25 °C, in a movement cell configuration consisting of a fuel chamber, a cathodic chamber, and an anodic chamber. The as-prepared working electrode was fastened between the fuel and cathodic chambers, with the catalyst layer facet going through the cathodic chamber (geometric energetic floor space of 1 cm²). The Fe-S/Ni foam electrode and the Hg/HgO electrode (with 1 M KOH because the filling answer) have been employed as counter and reference electrodes. An anion trade membrane (AEM) (Fumatech FAB-PK-130) was used to separate the cathode and the anode chambers.

The mixed catalyst and diffusion layer, anion trade membrane and nickel anode have been then positioned and clamped collectively utilizing polytetrafluoroethylene (PTFE) spacers such that alkaline electrolytes could possibly be launched into the chambers between the anode and membrane in addition to the membrane and the cathode at 10 mL·min⁻¹ utilizing a peristaltic pump. The CO (Air France, 99.99%) movement was stored fixed at 20 mL·min⁻¹ utilizing Alicat Scientific mass movement controller after which equipped to the fuel chamber. The precise movement charge was decided utilizing a bubble flowmeter on the outlet of cathodic chamber.

The MEA electrolysis was carried out at 25 °C, in a home-made 5 cm² CO electrolyzer. An as-prepared gas-diffusion electrode (2.0 cm × 2.5 cm) was employed because the cathode, and a PTFE insulator sheet with a 5 cm² window was connected to the cathode to keep away from brief circuit. A pre-treated Sustainion membrane (X37-FA) and a Fe-S/Ni foam electrode (2.0 cm × 2.5 cm) have been placed on the highest of the membrane. Then, 1 M KOH aqueous answer was used because the anolyte and circulated utilizing a pump at a charge of 30 ml min⁻¹. On the cathode facet, CO fuel (40 mL·min⁻¹) was constantly humidified with DI water and fed into the cathode chamber. The fuel merchandise have been collected and examined by an in-line fuel chromatograph geared up with a chilly entice. Because of the liquid product crossover, the FEs of liquid merchandise have been calculated utilizing the whole quantity of the merchandise collected at anodes and cathodes.

The Fe-S/Ni foam electrodes have been fabricated by a solvothermal methodology. Sometimes, Fe-S/Ni foam (Shenzhen Poxon Equipment Know-how Co. Ltd., floor density: 350 g m⁻², thickness: 1.5 mm, dimension: 3.0 × 4.0 cm²) was ultrasonicated in acid, acetone and ethanol. Ferric chloride hexahydrate (4.87 g) and sodium sulfide nonahydrate (7.21 g) have been first dissolved in 300 ml deionized water, below stirring for two h at room temperature. Then 35 ml combination and Ni foam after pretreatment have been transferred right into a Teflon-lined stainless-steel autoclave (50 mL) for a solvothermal remedy at 150 °C for 13.5 h, and subsequently centrifuged thrice with deionized water. The pattern was ultimate dried in a vacuum oven at 60 °C for 12 h.

All CO discount experiments have been carried out utilizing an electrochemical workstation (Autolab PGSTAT302N) geared up with a ten A present booster. The reactions have been run for not less than 300 s earlier than the merchandise have been collected for evaluation to verify the pre-catalysts have been utterly electro-reduced to a secure state because the CORR catalysts. Fuel chromatograph (Agilent Applied sciences 7890B or Shanghai Ramiin GC 2060) geared up with thermal conductivity (TCD) and flame ionization (FID) detectors have been used to find out the gaseous merchandise, which have been collected from each the outlet of fuel chamber and cathode chamber to make the fuel check extra correct. The liquid merchandise have been analyzed offline utilizing ¹H nuclear magnetic resonance (NMR) evaluation (AVANCE III HD 400 MHz). Dimethyl sulfoxide (Sigma, 99.99%) was added as an inside normal for NMR evaluation. The one-dimensional ¹H spectrum was measured with water suppression utilizing a pre-saturation methodology. The Faradaic efficiencies (FEs) of liquid merchandise have been calculated based mostly on the whole quantity of the merchandise collected in anode and cathode sides throughout the identical interval as a result of liquid crossover. After acquiring the n-propanol focus of every pattern from NMR quantification, FE_n-propanol was calculated based mostly on the next equation:

the place i is the stabilized complete present throughout electrolysis measurements.

Electrochemical energetic floor space (ECSA) calculation

The ECSAs of catalysts have been calculated based mostly on their electrical double layer capacitor (C_dl), which have been obtained from CV plots in a slender non-Faradaic potential window from 0.14 to 0.20 V (vs. RHE). The measured capacitive present densities at 0.17 V have been plotted as a perform of scan charge and the slope of the linear match was calculated as C_dl. The particular capacitance was discovered to be 29 μF cm⁻², and the ECSA of the catalyst is calculated from the next equation:

The intrinsic exercise was revealed by normalizing the present to the ECSA to exclude the impact of floor space on catalytic efficiency. The ECSA values of the catalysts are listed in Supplementary Desk 4.

Cathodic vitality effectivity (EE) calculation

Cathodic EE is calculated assuming the overpotential of anodic oxygen evolution response to be zero, which is calculated as follows:

the place E is the utilized potential; FE_n-propanol is the measured Faradaic effectivity of n-propanol; E_n-propanol is the thermodynamic potential of the CO-to-n-propanol course of, i.e., 0.20 V. This potential is introduced with out iR correction, besides in Supplementary Desk 9, the place a 70% iR correction was carried out. The uncompensated answer resistances (R_Ω) have been measured by extrapolating the electrochemical impedance semi-circle to the high-frequency finish, which was ca. 3.5 Ω for every electrode in 1 M KOH.

Full-cell EE calculation

Just like cathodic vitality EE, full-cell EE is calculated as follows:

the place E_cell is the measured cell voltage at a given present density, FE_n-propanol is the measured Faradaic effectivity of n-propanol; E_n-propanol is the thermodynamic potential of the CO-to-propanol course of, i.e., 0.20 V.

DFT calculations

The Vienna ab initio simulation package deal (VASP)^64,65,66 was used for all density practical idea (DFT) calculations. The 1 s electron in H, the two s, 2p electrons in C and O, the threed, 4p electrons in Cu, and the 6 s, 6p electrons in Pb have been handled as valence electrons, whereas the kinetic vitality cutoff for the plane-wave foundation units was set to be 400 eV. The remaining core electrons have been described by the projector augmented-wave (PAW) methodology⁶⁷. The Monkhorst–Pack meshes⁶⁸ of two × 2 × 1 k-point sampling within the Brillouin zone have been employed for the slab mannequin. For the pristine Cu(100), a 4 × 4 supercell (10.2 Å × 10.2 Å) consisting of two fastened backside layers and a couple of relaxed high layers was used. For the pristine Cu(211) and Pb-doped Cu(211) floor, a 2 × 4 supercell (12.5 Å × 10.2 Å) consisting of 6 fastened backside layers and 6 relaxed high layers was used. When the convergence criterion for optimizations was met, the biggest remaining pressure on every atom was lower than 0.03 eV Å⁻¹. For all calculations, the generalized gradient approximation (GGA) of the Perdew–Burke–Ernzerhof (PBE) practical was used⁶⁹.

For CO discount mechanism, there have been proton-coupled electron switch (PCET) steps. The Gibbs free vitality change (ΔG) was calculated through the use of the usual hydrogen electrode (SHE) mannequin^70,71, which used one-half of the chemical potential of hydrogen because the chemical potential of the proton-electron pair. In accordance with this methodology^70,71, the ΔG worth was decided as:

the place ΔH and ΔS have been the enthalpy change and the entropy change, respectively. ΔG_U was the free vitality contribution associated to the electrode potential U. T is absolutely the temperature. ΔG_pH was the focus correction to the H⁺ free vitality, which was calculated as

the place okay_B is the Boltzmann fixed. Because the theoretical overpotential was impartial of the pH or the potential worth U⁷², the evaluation for the free vitality modifications was carried out at normal circumstances (pH = 0, T = 298.15 Okay, 1 atm) and U = 0. Throughout calculations, for comfort, we assumed the chemical potential of the water in answer was equal to three.169 kPa, the identical as pure liquid water at room temperature.

We assumed that along with the whole digital energies, the interpretation and rotation contributions of the fuel part have been important whereas different elements have been ignored. Assuming the fuel part to be a really perfect fuel, the partition features of translation ({Q}^{trans}) and rotation ({Q}^{rot}) have been calculated as⁷³:

the place P and m are the strain and the molecular mass, respectively, okay_B is the Boltzmann fixed, and T (298.15 Okay) is absolutely the temperature. (V=frac{{okay}_{B}T}{P}) is the amount of the system, ({{{{{rm{sigma }}}}}}) is the symmetry issue, A^rot, B^rot, C^rot are rotational constants, and h is the Plank’s fixed.

Ab initio molecular dynamics (AIMD) simulations based mostly on Born-Oppenheimer approximation have been additionally carried out utilizing VASP^64,65,66. A time step of two fs was used. Canonical (NVT) ensemble and Nosé-Hoover thermostats^74,75 have been set to 600 Okay. Within the current work, the MD simulation was solely used to discover the potential secure constructions for the Pb-Cu floor as an alternative of acquiring free vitality. Subsequently, the temperature was not essential to be set at room temperature the place experiment was carried out. The comparatively excessive temperature MD simulation was employed as a result of the trajectory was straightforward to entice in some native minimal at low temperature, which was not superb for looking the extra secure constructions. After MD simulations, the low vitality constructions within the trajectory have been picked out and optimized by the conventional DFT calculations described above.