MaterialsAluminum foil (99.999%), Gold foil (99.99%), Copper foil (99.99%) were purchased from Beijing Jiaming Platinum Nonferrous Metals Co., Ltd. Phenylacetylene (97%), Styrene (99%), 1,4-dioxane (99.7%), Tert butanol (99.5%) were purchased from Adamas. KOH (95%) were purchased from Greagent. KCl (99.5%) and Nitric Acid (67%) were purchased from Sinopharm Co. Ltd. All chemicals were used without further purification.Preparation of CuAu nanoporous alloyAl80Cu18Au2 ribbons were prepared via a melt-spinning process. The precursor ribbons were then chemically etched via two-step dealloying method. Firstly, 200 mg of Al80Cu18Au2 ribbons was put into 200 ml of 2 M KOH aqueous solution to remove partial of Al in the ribbons. The etching reaction was kept at 30 °C for around 10 h until no apparent bubbles were observed. As shown in the X-ray powder diffraction (XRD) pattern, the obtained product from the first-step dealloying was composed of Cu18Au2, Cu2O and Al2Cu3 phases. The as-prepared product was washed with ultra-pure H2O for several times till the solution became neutral. After that, the second-step dealloying treatment was carried out by adding the obtained product into 200 ml of 0.5 M HNO3 aqueous solution kept at 30 °C, Cu2O was thoroughly removed. At the same time, residues Al2Cu3 phase were selectively removed from the first ordered pore structure. After 2 h, Hnp-Cu50Au50 alloy was obtained. After washing process, the product was dried in vacuum oven at 60 °C for 24 h for further structure characterization and electrocatalytic analysis. Hnp-Cu70Au30 and Hnp-Cu35Au65 alloys were prepared with the same reaction conditions except the reaction times of the second-step dealloying were changed to 1 and 3 h, respectively. For comparison, unimodal nanoporous Cu, Au, and Cu50Au50 were fabricated by dealloying Al80Cu20, Al80Au20, and Al80Cu10Au10 ribbons in 2 M KOH at 30 °C for 10 h, respectively.CharacterizationsXRD patterns of the samples were conducted by using a Bruker D8 Advance X-ray diffractometer with Cu Kα radiation (λ = 1.5418 Å). Morphology and chemical composition were collected via MIR3 TESCAN SEM equipped with an Oxford energy dispersive X-ray spectroscope. HAADF-STEM and EDS mapping were conducted on a JEM-ARM 200F with double spherical aberration (Cs) correctors for both the probe forming and image-forming objective lenses at an accelerating voltage of 200 kV. The chemical state and composition of the samples were characterized using XPS (Thermo Scientific Escalab 250Xi) with an Al Kα monochromatic (150 W, 20 eV pass energy, 500 μm spot size). The content of K+ were carried out via ICP-OES (Atom scan Advantage, Thermo Jarrell Ash).Operando X-ray absorption spectraThe XAS experiments were carried out at Beamline 01C1 at Taiwan Synchrotron Radiation Research Center. A home-made Teflon electrochemical cell with electrochemical workstation (Ivium, Compact Stat.) was employed for operando XAS measurement under the sensitive fluorescence model. Adding phenylacetylene to a cell filled with 1.0 M KOH electrolyte. A graphite rod was used as the counter electrode and a Hg/HgO electrode was used as the reference electrode. The carbon paper loaded with catalyst as the working electrode was in contact with Kapton tape to the observation window of the cell. During the experimental measurement, different potentials of OCV, −0.3 and −0.5 V vs. RHE were applied to the system and each potential was maintained to collect spectra for 30 min. The acquired XAS data were processed using Athena software. All the voltage indicated in the “Methods” section has not been iR corrected.Electrochemical measurementsElectrochemical measurements were carried out in a divided three-compartment electrochemical cell consisting of a working electrode, a carbon rod counter-electrode, and a Hg/HgO reference electrode. The cathode cell and anode cell containing 1.0 M KOH with or without 1 M KCl solution, respectively, were separated by a Nafion 117 proton exchange membrane. 1 mmol of alkynes dissolved in dioxane were added into the cathode and stirred to form a homogeneous solution (16 ml 1.0 M KOH + 1 M KCl and 4 ml dioxane). Then, chronoamperometry was carried out at a given constant potential and stirred until the starting substrates disappeared. The liquid products were extracted with ethyl acetate and then quantified by gas chromatography (Shimadzu, GC-2010 Plus) equipped with a flame ionization detector (FID). In a typical procedure of the fabrication of the working electrode, the catalyst ink was prepared by dispersing 5 mg of catalysts into a mixture solution of 0.48 ml ethanol and 20 μl of Nafion solution (5%, w/w, Alfa Aesar) with sonication for 30 min. Fifty μl of the electrocatalyst ink was loaded onto a carbon paper with an area of 1 × 1 cm2 by drop-coating with the loading mass of catalyst is 0.50 mg cm−2. The as-prepared catalyst film was dried at room temperature.Quantitative reductive productThe conversion (%), selectivity (%), and Faradaic efficiency (FE, %) of alkenes were calculated using Eqs. (1)–(3):$${{{{{\rm{Conversion}}}}}} \, (\%)=\frac{{{{{{\rm{mol}}}}}}\; {{{{{\rm{of}}}}}}\; {{{{{\rm{formed}}}}}}\; {{{{{\rm{alkene}}}}}}}{{{{{{\rm{mol}}}}}}\; {{{{{\rm{of}}}}}}\; {{{{{\rm{initial}}}}}}\; {{{{{\rm{alkyne}}}}}}}\times 100\%$$
(1)
$${{{{{\rm{Selectivity}}}}}} \, (\%)=\frac{{{{{{\rm{mol}}}}}}\; {{{{{\rm{of}}}}}}\; {{{{{\rm{formed}}}}}}\; {{{{{\rm{alkene}}}}}}}{{{{{{\rm{mol}}}}}}\; {{{{{\rm{of}}}}}}\; {{{{{\rm{consumed}}}}}}\; {{{{{\rm{alkyne}}}}}}}\times 100\%$$
(2)
$${{{{{\rm{FE}}}}}} \, (\%)=\frac{{{{{{\rm{nmF}}}}}}}{{{{{{\rm{It}}}}}}}\times 100\%$$
(3)
where n = number of transferred electrons; m = amount of substance; F = Faraday’s constant; I = total current; t = electrolysis time.Calculation of energy efficiencyThe energy efficiency (EE) was defined as the ratio of fuel energy to applied electrical power, which was calculated by:$${{{{EE}}}}_{{{{styrene}}}}=(({{E}^{\theta }}_{{{{OER}}}}\,-\,{{E}^{\theta }}_{{{{styrene}}}}) \, \times \, {{{{FE}}}}_{{{{styrene}}}})/({E}_{{{{OER}}}}\,-\,{E}_{{{{styrene}}}})$$
(4)
where Eθstyrene represents the equilibrium potential of phenylacetylene electroreduction to styrene, which is calculated by DFT (0.49 V vs. RHE) (Supplementary Fig. 26)6, EθOER is the equilibrium potential of the oxygen evolution reaction (OER) (1.23 V vs. RHE), FEstyrene is the Faradaic efficiency for styrene, and EOER and Estyrene are the applied potentials.Surface-adsorbed K+
Hnp-Cu50Au50 and np-Cu50Au50 were run in 1.0 M KOH at −0.4 V vs. RHE. After 2 min, the electrode was directly raised above the electrolyte and transferred into 5 ml pure water, during which the voltage was kept. After immersing in water, the voltage was removed to release any adsorbed K+ from the electrode. The transferred electrodes from the same aqueous solution without applying voltage were used as the blank background. Subsequently, the amount of K+ in the water was determined using an inductively coupled plasma optical emission spectrometer (ICP-OES, Atom scan Advantage, Thermo Jarrell Ash, USA). Finally, the amount of K+ in ultrapure water with the background deducted represents the true amount of K+ adsorbed on the surface of the Hnp-Cu50Au50 and np-Cu50Au50 catalysts. The obtained results were normalized by ECSA for comparison.Scavenge of high active H* with t-BuOHA total of 1 mmol of phenylacetylene was added into the electrolytic cell for the following semi-hydrogenation with/without t-BuOH. Chronoamperometry was carried out at a given constant potential −0.6 V vs. RHE for 210 min in 1 M KOH. The content of styrene was detected every 30 min.Calculation of the electrochemically active surface areas (ECSA)ECSA was calculated from the equation as follow:$${{{ECSA}}}=\frac{{C}_{{{{dl}}}}}{{C}_{s}}$$
(5)
The electrochemical double layer capacitance (Cdl) was measured by CV curves at different scan rates (Supplementary Fig. 21) and the general specific capacitance (Cs) found to be 60 μF cm−2 in 1.0 M KOH.COMSOL Multiphysics simulationsThe electric field and K+ concentration within the vicinity of Cu50Au50 electrodes were simulated by solving the Poisson-Nernst-Planck equations using the COMSOL Multiphysics finite-element-based solver (https://www.comsol.com/). The structure models for catalyst particles with representative pore sizes (5.0 nm and 80 nm) were constructed based on the experimental SEM images to perform finite-element-method (FEM) simulations.The electric field (E) distribution was described by the following equation:$${{E}}=- \! \nabla V$$
(6)
$$\rho={\varepsilon }_{r}{\varepsilon }_{0}\nabla \, {{\cdot }}\, E$$
(7)
where V, ρ, εr, and ε0 represent the applied potential bias, charge density, dielectric in vacuum and materials, respectively. E was the negative gradient of the electric potential.We choose the bulk solution as the grounding condition for the electrolyte potential:The ion absorption behavior was described by the Nernst–Planck equations:$$\nabla \,{{\cdot }}\, ({Di}\nabla {ci}+\frac{{DiziF}}{{RT}}{ci}\nabla \psi ) \,=\, 0$$
(9)
where c, D, z are the ion concentrations, diffusion coefficients, ion valences, respectively. In addition, F, R, and T represent the Faraday’s constant, gas constant, and absolute temperature (T = 293.15 K), respectively, and ψ is the electrostatic potential that satisfies the Poisson equation49.Computational methodsFirst-principles calculations were implemented using Vienna Ab-initio Simulation Package (VASP 5.4.4)50,51, with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional of generalized gradient approximation (GGA). The basis set utilized projector-augmented-wave pseudopotential (PAW) method, and the energy cut off was set at 400 eV52,53. Convergence was assumed when forces on each atom was less than 0.02 eV/Å and the self-consistent field (SCF) tolerance was 10−5 eV in the geometry optimization. The DFT-D3 method with Grimme’s scheme was employed to correct the van der Waals interactions54. In the calculations, the pure Cu and Au surface were modeled by three-layer (111) fcc slabs with a 6 × 6 supercell, and a 4 × 4 supercell of CuAu (110) with three atomic layers was considered for the CuAu Alloy. For the Brillouin zone integration, a Monkhorst-Pack k-point mesh of 2 × 2 × 1 was employed. Here, the top two atomic layers were relaxed, and all the atoms at the bottom were frozen. To avoid the interactions between periodic structure, the vacuum space of 20 Å was employed along the z direction.As an indicator for each elemental step of phenylacetylene semi-hydrogenation, the Gibbs free energy (G) is calculated by:$${{{{{\rm{G}}}}}} \,=\, E+{E}_{{{{ZPE}}}}+\int {C}_{p}{dT}-{TS}$$
(10)
where \(E\) is the DFT-optimized total energy, \({E}_{{{{{{{\rm{ZPE}}}}}}}}\) is the zero-point vibrational energy, \({C}_{p}\) is the heat capacity, \(T\) = 298.15 K is the temperature and \(S\) is the entropy. All corrections of Gibbs free energy were obtained using VASPKIT (v.1.1.2) software55.
Alloying and confinement effects on hierarchically nanoporous CuAu for efficient electrocatalytic semi-hydrogenation of terminal alkynes
