Enhancement in hydrogen evolution using Au-TiO(2) hollow spheres with microbial devices modified with conjugated oligoelectrolytes

OBJECTIVE: Although 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. METHODS: The 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-TiO(2) hollow spheres and conjugated oligoelectrolytes were synthesised chemically and introduced to the PEC cell and MFC, respectively. Hydrogen evolution measurements were performed in triplicates. RESULTS: The hybrid PEC–MFC platform generated a photocurrent density of 0.35 mA/cm(2) (~70× enhancement) as compared with the stand-alone P25 standard PEC cell (0.005 mA/cm(2)) under one-sun illumination (100 mW/cm(2)) at zero bias (0 V vs. Pt). This increase in photocurrent density was accompanied by continuous H(2) production. No H(2) was observed in the P25 standard PEC cell whereas H(2) evolution rate was ~3.4 μmol/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-TiO(2) hollow spheres electrode. CONCLUSIONS: The 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.