PhD student, Fundación Universidad de las Américas Puebla
This topic aims to develop a wastewater treatment method that generates hydrogen as an added value.
Most of the contaminants in wastewater have chemical energy that can be transformed to be usable; if wastewater treatment can do this, we would have another consistent renewable energy source in addition to the clean water that current plants produce.
Abstract: The kinetics of photoelectrochemical (PEC) oxidation of methanol, as a model organic substrate, on α-Fe2O3 photoanodes are studied using photo-induced absorption spectroscopy and transient photocurrent measurements. Methanol is oxidized on α-Fe2O3 to formaldehyde with near unity Faradaic efficiency. A rate law analysis under quasi-steady state conditions of PEC methanol oxidation indicates that rate of reaction is second order in the density of surface holes on hematite and independent of the applied potential. Analogous data on anatase TiO2 photoanodes indicate similar second order kinetics for methanol oxidation with a second order rate constant two orders of magnitude higher than on α-Fe2O3. Kinetic isotope effect studies determine that the rate constant for methanol oxidation on α-Fe2O3 is retarded ~ 20 fold by H/D substitution. Employing these data, we propose a mechanism for methanol oxidation under one sun irradiation on these metal oxide surfaces and discuss the implications for the efficient PEC methanol oxidation to formaldehyde and concomitant hydrogen evolution.
Pub.: 25 Jul '17, Pinned: 31 Aug '17
Abstract: Hematite (α-Fe2O3) is a suitable candidate for photoelectrochemical water splitting due to its well-suited band structure, stability, and availability. However, water splitting using a low external potential is the major challenge that limits the practical application of hematite. Here, we achieve a very low onset potential using a sequential surface treatment approach to overcome two fundamental limiting factors, sluggish hole transfer, and interfacial recombination, independently. First, a heavily doped Fe2-xSnxO3 surface passivation layer was created by Sn(4+) surface treatment which can robustly inhibit interfacial recombination. Then, an NiOOH catalyst layer was deposited that greatly enhances the charge transfer process across the passivated electrode/electrolyte interface. By exploiting this approach, the optimized sequentially treated photoanode (Fe2O3/Fe2-xSnxO3/NiOOH) exhibits a low photocurrent onset potential of 0.49 V vs. RHE and a saturated photocurrent density of 2.4 mA cm(-2) V at 1.5 V vs. RHE. Transient photocurrent and impedance spectroscopy measurements further reveal that the combined Fe2-xSnxO3/NiOOH layers reduce interfacial recombination and enhance charge transfer across the electrode/electrolyte interface. The results provide convincing evidence that it is possible to address the problems of surface trap recombination and sluggish catalysis independently by employing surface passivation layers first and catalysts later sequentially.
Pub.: 27 Jul '17, Pinned: 31 Aug '17
Abstract: We report a self-biased, solar-driven microbial photoelectrochemical cell (solar MPC) that can produce sustainable energy through coupling the microbial catalysis of biodegradable organic matter with solar energy conversion. The solar MPC consists of a p-type cuprous oxide nanowire-arrayed photocathode and an electricigen (Shewanella oneidensis MR-1)-colonizing anode, which can harvest solar energy and bioenergy, respectively. The photocathode and bioanode are interfaced by matching the redox potentials of bacterial cells and the electronic bands of semiconductor nanowires. We successfully demonstrated substantial current generation of 200 μA from the MPC device based on the synergistic effect of the bioanode (projected area of 20 cm2) and photocathode (projected area of 4 cm2) at zero bias under white light illumination of 20 mW/cm2. We identified the transition of rate-limiting step from the photocathode to the bioanode with increasing light intensities. The solar MPC showed self-sustained operation for more than 50 h in batch-fed mode under continuous light illumination. The ability to tune the synergistic effect between microbial cells and semiconductor nanowire systems could open up new opportunities for microbial/nanoelectronic hybrid devices with unique applications in energy conversion, environmental protection, and biomedical research.
Pub.: 14 Oct '10, Pinned: 31 Aug '17
Abstract: Here we demonstrate the feasibility of continuous, self-sustained hydrogen gas production based solely on solar light and biomass (wastewater) recycling, by coupling solar water splitting and microbial electrohydrogenesis in a photoelectrochemical cell-microbial fuel cell (PEC-MFC) hybrid device. The PEC device is composed of a TiO2 nanowire-arrayed photoanode and a Pt cathode. The MFC is an air cathode dual-chamber device, inoculated with either Shewanella oneidensis MR-1 (batch-fed on artificial growth medium) or natural microbial communities (batch-fed on local municipal wastewater). Under light illumination, the TiO2 photoanode provided a photovoltage of ~0.7 V that shifted the potential of the MFC bioanode to overcome the potential barrier for microbial electrohydrogenesis. As a result, under light illumination (AM 1.5G, 100 mW/cm(2)) without external bias, and using wastewater as the energy source, we observed pronounced current generation as well as continuous production of hydrogen gas. The successful demonstration of such a self-biased, sustainable microbial device for hydrogen generation could provide a new solution that can simultaneously address the need of wastewater treatment and the increasing demand for clean energy.
Pub.: 13 Sep '13, Pinned: 31 Aug '17