Phase‐Contact Engineering in Mono‐ and Bimetallic Cu‐Ni Co‐catalysts for Hydrogen Photocatalytic Materials

Abstract

Understanding how a photocatalyst modulates its oxidation state, size, and structure during a photocatalytic reaction under operando conditions is strongly limited by the mismatch between (catalyst) volume sampled by light and, to date, the physicochemical techniques and probes employed to study them. A synchrotron micro-beam X-ray absorption spectroscopy study together with the computational simulation and analysis (at the X-ray cell) of the light-matter interaction occurring in powdered TiO -based monometallic Cu, Ni and bimetallic CuNi catalysts for hydrogen production from renewables was carried out. The combined information unveils an unexpected key catalytic role involving the phase contact between the reduced and oxidized non-noble metal phases in all catalysts and, additionally, reveals the source of the synergistic Cu-Ni interaction in the bimetallic material. The experimental method is applicable to operando studies of a wide variety of photocatalytic materials.

Devisable POM/Ni Foam Composite: Precisely Control Synthesis toward Enhanced Hydrogen Evolution Reaction at High pH

“…The Co K-edge XANESs pectra of NiCo-POM/Ni, Co 3 O 4 and Co foil were presented in Figure4.B yc omparing the Co K-edge of NiCo-POM/Ni sample with that of Co and Co 3 O 4 ,t he NiCo-POM/Nie xhibitedaslight shiftt ol ower energy,i ndicating the + 2o xidation state of Co in the NiCo-POM. [37,38] It was consistent with that of XPS results. The Co K-edge k 3 c(k)o scillation curve ( Figure 4c)d isplayed that the oscillation amplitude of NiCo-POM/Ni was smaller than those observedi nt he Co 3 O 4 and Co foil, indicating structurald ifference in the coordination environment surrounding the Co atoms.…”

“…The Co K‐edge XANES spectra of NiCo‐POM/Ni, Co 3 O 4 and Co foil were presented in Figure . By comparing the Co K‐edge of NiCo‐POM/Ni sample with that of Co and Co 3 O 4 , the NiCo‐POM/Ni exhibited a slight shift to lower energy, indicating the +2 oxidation state of Co in the NiCo‐POM . It was consistent with that of XPS results.…”

Photocatalysis for Hydrogen Production and CO2 Reduction: The Case of Copper‐Catalysts

“…In this regard, in‐situ and operando characterization methodologies can offer real advantages in materials characterization and expand our knowledge on the physicochemical properties of photocatalysts under real catalytic and synthetic conditions ,. For example, operando X‐ray absorption spectroscopy revealed that the oxidation of Cu in monometallic Cu and bimetallic Cu/Ni particles deposited on anatase TiO 2 applied in H 2 production is critically affected by the irradiation, the reaction environment and the distance from the surface of the particle . Starting from the fully reduced Cu state, under real catalytic conditions (i. e. irradiation and reaction media) a core‐shell structure was observed where the metallic Cu (core) facilitated the electron handling properties while oxidized Cu species had the surface chemical role …”

Operando Spectroscopy in Photocatalysis

“…The three panels of Figure thus display the pseudo superficial rate of photon absorption for on‐top illumination and for three titania (anatase type) powders as a function of the depth from the surface of the materials located in a situ cell typically used for XAS (X‐ray absorption spectroscopy) or DIFTS (diffuse infrared Fourier transform spectroscopy) measurements. The central panel provides a result corresponding to the optical properties of a typical anatase sample while the extremes show values dividing (left panel) or multiplying (right panel) by 2 the absorption coefficient of the material represented in the central panel . Two (maximum and minimum) limits for the optical properties titania (absorption coefficient ) are thus represented in Figure , roughly covering “all” values experimentally observed for anatase samples ,.…”

“…The central panel provides a result corresponding to the optical properties of a typical anatase sample while the extremes show values dividing (left panel) or multiplying (right panel) by 2 the absorption coefficient of the material represented in the central panel . Two (maximum and minimum) limits for the optical properties titania (absorption coefficient ) are thus represented in Figure , roughly covering “all” values experimentally observed for anatase samples ,. The color variation (as a function of the wavelength) normal to the illuminated surface is thus providing the variation in the photons absorbed at each point of a slide of the sample perpendicular to the incident light path.…”