Liquid metal-embraced photoactive films for artificial photosynthesis

Abstract

The practical applications of solar-driven water splitting pivot on significant advances that enable scalable production of robust photoactive films. Here, we propose a proof-of-concept for fabricating robust photoactive films by a particle-implanting technique (PiP) which embeds semiconductor photoabsorbers in the liquid metal. The strong semiconductor/metal interaction enables resulting films efficient collection of photogenerated charges and superior photoactivity. A photoanode of liquid-metal embraced BiVO₄ can stably operate over 120 h and retain ~ 70% of activity when scaled from 1 to 64 cm². Furthermore, a Z-scheme photocatalyst film of liquid-metal embraced BiVO₄ and Rh-doped SrTiO₃ particles can drive overall water splitting under visible light, delivering an activity 2.9 times higher than that of the control film with gold support and a 110 h stability. These results demonstrate the advantages of the PiP technique in constructing robust and efficient photoactive films for artificial photosynthesis.

Fig. 1. Particle implanting process for the fabrication of bioinspired photoelectrode film.

a The fabrication process of bioinspired semiconductor photoelectrode using an LMP metal, including (1) metal melting and (2) blade coating on a substrate to form a liquid metal film, (3) semiconductor particles (indicated by yellow spheres) casting on its surface, (4) roller-pressing the semiconductor particles into the liquid metal film, (5) liquid metal film solidification with cooling, and (6) achieving a monolayer-particle-embedded photoelectrode film by blowing off the loose particles on film surface. b Typical structure of a particle-post-assembly photoelectrode obtained from conventional methods (semiconductor particles deposited the conductive substrate in point-to-face contact manner) and the new type of bioinspired photoelectrode proposed in this work (semiconductor particles are embedded in the conductive metal layer and form three-dimensional intimate interfacial contact with the conductive layer). c The top-viewed scanning electron microscopy (SEM) image of the fabricated BiVO₄ photoelectrode using LMP metal. d The cross-sectional SEM image of the resultant BiVO₄ photoelectrode and the EDS mappings of Si, In, and V recorded on the cross-sectional SEM image.

Fig. 2. Photogenerated carrier regulation in the bioinspired photoactive film.

a–c SPVM images of typical BiVO₄ particles with well-developed facets assembled on FTO, on the surface of LMP metal film, and embedded in the metal film, respectively. d–f SPV curves plotted along the lines crossing over {011} and {010} facets in (a–c), respectively. g–i Photo-reduction deposition of MnO_x (MnO₄⁻ + e⁻ → MnO_x) on BiVO₄ particles with well-developed facets assembled on FTO, on the surface of LMP metal film and embedded in the LMP metal film, respectively. j–l Sketch maps of spatial separation of photogenerated carriers (electrons and holes) in the BiVO₄ particles with well-developed facets assembled on FTO, on the surface of LMP metal film, and embedded in the metal film, respectively.

Fig. 3. Performance of BiVO₄ particles embedded photoelectrode.

a The comparison of photocurrent density of the photoelectrodes of LMP metal embraced BiVO₄ particles (Metal–BiVO₄), LMP metal supported BiVO₄ particles (Metal/BiVO₄), the FTO-supported BiVO₄ particles (FTO/BiVO₄), and BiVO₄ particles in situ grown on FTO (FTO@BiVO₄) at 1.23 V_RHE. b The long-term stability of the BiVO₄ particle-embedded photoelectrode film with CoBi surface modification at a potential of 0.7 V_RHE. c The optical image of the BiVO₄ particle-embedded photoelectrode with a large size of 10 × 10 cm², in which nine local zones (1 × 1 cm² in area) at the center (#5), edges (#2, 4, 6, 8) and corners (#1, 3, 7, 9) were selected for the photo activity measurements, and different areas (1 × 1, 2 × 2, 3 × 3, 4 × 4, 5 × 5, 6 × 6, 7 × 7 and 8 × 8 cm²) at the center were chosen for the assessment of “area effect”. d The photocurrent densities of the nine local zones in the photoelectrode after decorating a CoBi cocatalyst at 1.23 V_RHE. e The photocurrents recorded on different areas of the BiVO₄ particle-embedded photoelectrode and the corresponding photocurrent density retentions of operation zones with different areas at 1.23 V_RHE. f The photocurrent decay curves were recorded from the 64 cm² operation area at 1.23 V_RHE.

Fig. 4. Application of the LMP metal-based PiP process to fabricate Z-scheme photoactive film for artificial photosynthesis.

a Schematic of Z-scheme photoactive film with two types of semiconductors (HERP/OERP) embedded in the LMP liquid metal matrix for artificial photosynthesis. b Schematic of water splitting reactions occurring on the Z-scheme photoactive film with two types of semiconductors (HERP/OERP) embedded in the LMP liquid metal matrix. c Optical image of the Z-scheme photoactive film comprising of faceted BiVO₄ and Rh:SrTiO₃ particles embedded in the LMP liquid metal matrix. d The top-view SEM image of the fabricated Z-scheme photoactive film using the LMP metal-based PiP technique. e, f The EDS mapping images of Sr and V recorded on the top-view SEM image. g The Fermi energy level positions of different materials. h The photocatalytic production of H₂ and O₂ from water splitting with the Z-scheme photoactive films, comprising of Rh:SrTiO₃ and BiVO₄ particles embedded in the LMP liquid metal matrix (left panel) and supported on the Au film (right panel), under visible light (≥420 nm) irradiation. i The cycling performance of photocatalytic water splitting conducted with the LMP metal-based Z-scheme photoactive film.

Fig. 5. Advantages of the LMP metal-based PiP technique for the synthesis of photoactive films.

a The short-circuit photocurrent density enhancement of the photoelectrodes (Metal–ZnO, Metal–WO₃, Metal–Cu₂O) of LMP metal embraced particles relative to the control photoelectrodes (FTO/ZnO, FTO/WO₃, FTO/Cu₂O) assembled on FTO for commercial ZnO, WO₃, and Cu₂O powders and the micro-/nanostructured film photoelectrodes ((FTO/ZnO-G, FTO/WO₃-G, FTO/Cu₂O-G; G from grown) of ZnO, WO₃, and Cu₂O in situ grown on the FTO substrate. b The short-circuit photocurrent densities of the particles-embedded photoelectrodes from commercial WO₃ powder on different substrates (quartz, board, cloth, paper, and Ti mesh). c Schematic of scalable fabrication of the LMP metal embraced photoactive films on PET from commercial semiconductor (ZnO, WO₃, and Cu₂O) powders using an industrial roll-to-roll process. d The PEC performance of the WO₃ particles-embedded photoelectrode film on PET for the cyclic bending tests. The inset is the optical image of the film photoelectrode assembled on a PET substrate under bending conditions and the schematical image of a bending cycle of the photoelectrode. e The optical images of a 100 mm × 100 mm film of BiVO₄ and Rh:SrTiO₃ semiconductor particles embedded in Field’s metal on a glass substrate and the raw materials retrieved from the film by ultrasonication treatment in a hot water bath. f The photocatalytic overall water splitting activity of BiVO₄ and Rh:SrTiO₃ particles-embedded photoactive film assembled with the retrieved Field’s metal under visible light (≥420 nm) irradiation.