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Enhanced Photocatalytic Hydrogen Evolution from Transition-Metal Surface-Modified TiO₂.

ABSTRACT: This study describes the UV solution photodeposition of several earth-abundant 3d transition metals (Co, Ni, and Cu) onto the surface of nanoparticulate TiO₂. Irradiated methanolic metal dichloride solutions with suspended Degussa P25-TiO₂ (1-2 wt % metal to TiO₂) yield visibly colored titanias, whereas the bulk TiO₂ structure is unchanged; X-ray photoelectron spectroscopy confirms that metals are present on the titania surface in either reduced metal (Cu/Cu⁺) or metal cation states (Co²⁺ and Ni²⁺), and UV-vis diffuse reflectance spectroscopy shows new visible absorbance features. The analyzed bulk metal contents (?0.04-0.6 at. %, highest for copper) are lower than the nominal metal solution content. Mixed-metal solution photodeposition reactions roughly parallel observations for single metals, with copper deposition being most favored. These 3d metal surface-modified titanias show significant (?5-15×) improvement in UV photocatalytic H₂ evolution versus unmodified TiO₂. H₂ evolution rates as high as 85 ?mol/h (8500 ?mol h^-1 g^-1) were detected for Cu-coated TiO₂ using continuous monitoring of reactor headspace gases by portable mass spectrometry. Control experiments verify the necessity of the methanol sacrificial oxidant in both metal deposition and H₂ evolution. In situ metal surface deposition is quickly followed by enhanced H₂ evolution relative to TiO₂, but at lower levels than isolated metal surface-modified titanias. The photodeposited 3d metal species on the TiO₂ surface likely act to reduce electron-hole recombination by facilitating the transfer of photoinduced TiO₂ conduction band electrons to protons in solution that are reduced to H₂. This study demonstrates a facile method to modify photoactive TiO₂ nanoparticles with inexpensive 3d transition metals to improve photocatalytic hydrogen evolution, and it shows the utility of quantitative real-time gas evolution monitoring by portable mass spectrometry.

SUBMITTER: Montoya AT

PROVIDER: S-EPMC6641314 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature

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Enhanced Photocatalytic Hydrogen Evolution from Transition-Metal Surface-Modified TiO2.

Montoya Anthony T AT Gillan Edward G EG

ACS omega 20180312 3

This study describes the UV solution photodeposition of several earth-abundant 3d transition metals (Co, Ni, and Cu) onto the surface of nanoparticulate TiO2. Irradiated methanolic metal dichloride solutions with suspended Degussa P25-TiO2 (1-2 wt % metal to TiO2) yield visibly colored titanias, whereas the bulk TiO2 structure is unchanged; X-ray photoelectron spectroscopy confirms that metals are present on the titania surface in either reduced metal ...[more]

PMID: 31458564

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Project description:ObjectiveAlthough photoelectrochemical (PEC) water splitting heralds the emergence of the hydrogen economy, the need for external bias and low efficiency stymies the widespread application of this technology. By coupling water splitting (in a PEC cell) to a microbial fuel cell (MFC) using Escherichia coli as the biocatalyst, this work aims to successfully demonstrate a sustainable hybrid PEC-MFC platform functioning solely by biocatalysis and solar energy, at zero bias. Through further chemical modification of the photo-anode (in the PEC cell) and biofilm (in the MFC), the performance of the hybrid system is expected to improve in terms of the photocurrent generated and hydrogen evolved.MethodsThe hybrid system constitutes the interconnected PEC cell with the MFC. Both PEC cell and MFC are typical two-chambered systems housing the anode and cathode. Au-TiO2 hollow spheres and conjugated oligoelectrolytes were synthesised chemically and introduced to the PEC cell and MFC, respectively. Hydrogen evolution measurements were performed in triplicates.ResultsThe hybrid PEC-MFC platform generated a photocurrent density of 0.35?mA/cm2 (~70× enhancement) as compared with the stand-alone P25 standard PEC cell (0.005?mA/cm2) under one-sun illumination (100?mW/cm2) at zero bias (0?V vs. Pt). This increase in photocurrent density was accompanied by continuous H2 production. No H2 was observed in the P25 standard PEC cell whereas H2 evolution rate was ~3.4??mol/h in the hybrid system. The remarkable performance is attributed to the chemical modification of E. coli through the incorporation of novel conjugated oligoelectrolytes in the MFC as well as the lower recombination rate and higher photoabsorption capabilities in the Au-TiO2 hollow spheres electrode.ConclusionsThe combined strategy of photo-anode modification in PEC cells and chemically modified MFCs shows great promise for future exploitation of such synergistic effects between MFCs and semiconductor-based PEC water splitting.

Dataset Information

Enhanced Photocatalytic Hydrogen Evolution from Transition-Metal Surface-Modified TiO₂.

Publications

Enhanced Photocatalytic Hydrogen Evolution from Transition-Metal Surface-Modified TiO<sub>2</sub>.

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