Photochemical Biofuel Cells

A photobioelectrochemical Fuel Cell (PBEC-FC) relies on the synergic effect of electroactive and photo-electroactive microorganisms with or without photosensitive electrode to degrade organic matter for diverse bioelectrochemical application. In addition to wastewater treatment, PBEC-FC is also versatile in producing bioelectricity, biofuel, and pollutant degradation. PBEC-FC can come with a different configuration to accommodate for various applications under specific reaction. As a result of continuous research, there are three developing configurations which are: photosynthetic-BFC (PS-BFC), photovoltaic BFC (PV-BFC), and photoelectrode-BFC (PE-BFC). Studies have demonstrated that light-driven BFC has improved the substrate oxidation in the anode and concurrent bioelectrochemical reaction in the cathode as compared to dark conditions. Motivated by the increasing number of publications for this technology, the various configurations of PBEC-FC that suit different applications and their performance will be discussed in this chapter. Although the current performance of PBEC-FC remains low, but, with a continuous advancement to develop a durable and high photoactive material, this green technology will be realized into practicality in the future

Experimental and theoretical study of Cu2 O photoelectrode and Cu2 O doped with Ag, Co, Ni and Zn metals for water splitting application

In the present study, cuprous oxide nanowire fabricated using wet chemical oxidation method was proven to produce high photoactive film for photoelectrochemical (PEC) water splitting. A relatively high photocurrent density of -5mA cm-2 at 0.6V vs Ag/AgCl was generated. The PEC performance is the reflection of intrinsic light absorption capacity at visible region which correspond to 2.0eV, an ideal band gap for PEC water splitting. Comparison with calculated data based on density functional theory using CASTEP shows that the band gap and light absorption capacity obtained from experimental work exhibited a close match. Hence, this study suggested that the preparation of Cu2 O thin film via wet chemical oxidation method obeyed the theoretical prediction. However, the Cu2 O is limited with poor stability in PEC condition attributed to the insufficient potential of its valence band to oxidize water. Therefore, an effort was directed to address the feasibility of shifting the valence band by modeling a doped Cu2 O with several dopants using DFT technique. The selected dopants were Ag, Co, Ni and Zn. Preliminary conclusion of this study indicated that doping could be used to tune the band gap of Cu2 O due to ionic radii of the dopant affected the shifting of band gap. In this study, Co showed more significant improvement of Cu2 O for photoelctrochemical water splitting process. However, to validate the simulation, further study should be carried out experimentally

High cell density fermentation of Candida rugosa on palm oil for lipase production and its mass transfer investigation / Mohd Nur Ikhmal bin Salehmin

Extracellular lipase of the yeast Candida rugosa was produced via high cell density fed-batch fermentations using palm oil as the sole source of carbon and energy. Feeding strategies consisted of a pH-stat operation, foaming-dependent control and specific growth rate control in different experiments. Compared to foaming-dependent feeding and the pHstat operation, the specific growth rate control of feeding proved to be the most successful. At the specific growth rate control set point of 0.05 h1, the final lipase activity in the culture broth was the highest at 700 U L1. This was 2.6-fold higher than the final enzyme activity obtained at a specific growth rate control set point of 0.15 h1. The peak enzyme concentration achieved using the best foaming-dependent control of feeding was around 28% of the peak activity attained using the specific growth rate control of feeding at 0.05 h1. Similarly, the peak enzyme concentration attained using the pH-stat feeding operations was a mere 9% of the peak activity attained by specific growth rate control of feeding at a setpoint of 0.05 h1. The highest biomass specific productivity of the enzyme was 0.19 U g1 h1 for the fed-batch operation with the specific growth rate controlled at 0.05 h1. Fedbatch fermentations were performed in a 2-L stirred-tank bioreactor (30 C, pH 7) with the dissolved oxygen level controlled at 30% of air saturation. Investigation on gas-liquid and liquid-liquid mass transfers by experimental and theoretical means was also carried out. The investigation was simulated in xanthan gum solution which resembles the viscosity of High Cell Density Fermentation (HCDF) at 1.68 mPa.s. Established correlations were successfully used to predict kLa value at different agitation rate ranging from 200-800 rpm for both oil and oxygen mass transfers under HCDF condition. However, the correlations failed to predict kLa value at the highest agitation rate used (1000 rpm) for liquid-liquid mass transfer

Synthesis of Cobalt Oxide on FTO by Hydrothermal Method for Photoelectrochemical Water Splitting Application

Cobalt oxide thin films were successfully grown directly on fluorine-doped tin oxide glass substrates through a simple, green, and low-cost hydrothermal method. An investigation into the physicochemical characteristics and photoelectrochemical (PEC) properties of the developed cobalt oxide thin film was comprehensively performed. At various annealing temperatures, different morphologies and crystal phases of cobalt oxide were observed. Microflowers (Co3O4) and microflowers with nanowire petals (Co3O4/CoO) were produced at 450 °C and 550 °C, respectively. Evaluation of the PEC performance of the samples in KOH (pH 13), Na2SO4 (pH 6.7), and H2SO4 (pH 1) revealed that the highest photocurrent −2.3 mA cm−2 generated at −0.5 V vs. reversible hydrogen electrode (RHE) was produced by Co3O4 (450 °C) in H2SO4 (pH 1). This photocurrent corresponded to an 8-fold enhancement compared with that achieved in neutral and basic electrolytes and was higher than the results reported by other studies. This promising photocurrent generation was due to the abundant source of protons, which was favorable for the hydrogen evolution reaction (HER) in H2SO4 (pH 1). The present study showed that Co3O4 is photoactive under acidic conditions, which is encouraging for HER compared with the mixed-phase Co3O4/CoO

Enhancing hydrogen production through anode fed-batch mode and controlled cell voltage in a microbial electrolysis cell fully catalysed by microorganisms

International audienceA microbial electrolysis cell (MEC) fully catalysed by microorganisms is an attractive technology because it incorporates the state-of-the-art concept of converting organic waste to hydrogen with less external energy input than conventional electrolysers. In this work, the impact of the anode feed mode on the production of hydrogen by the biocathode was studied. In the first part, three feed modes and MEC performance in terms of hydrogen production were evaluated. The results showed the highest hydrogen production under the continuous mode (14.6 ± 0.4), followed by the fed-batch (12.7 ± 0.4) and batch (0 L m(-2) cathode day(-1)) modes. On one hand, the continuous mode only increased by 15% even though the hydraulic retention time (HRT) (2.78 h) was lower than the fed-batch mode (HRT 5 h). A total replacement (fed-batch) rather than a constant mix of existing anolyte and fresh medium (continuous) was preferable. On the other hand, no hydrogen was produced in batch mode due to the extensive HRT (24 h) and bioanode starvation. In the second part, the fed-batch mode was further evaluated using a chronoamperometry method under a range of applied cell voltages of 0.3-1.6 V. Based on the potential evolution at the electrodes, three main regions were identified depending on the applied cell voltages: the cathode activation (<0.8 V), transition (0.8-1.1 V), and anode limitation (>1.1 V) regions. The maximum hydrogen production recorded was 12.1 ± 2.1 L m(-2) cathode day(-1) at 1.0 V applied voltage when the oxidation and reduction reactions at the anode and cathode were optimal (2.38 ± 0.61 A m(-2)). Microbial community analysis of the biocathode revealed that Alpha-, and Deltaproteobacteria were dominant in the samples with >70% abundance. At the genus level, Desulfovibrio sp. was the most abundant in the samples, showing that these microbes may be responsible for hydrogen evolution

Constructing bio-templated 3D porous microtubular C-doped g-C3N4 with tunable band structure and enhanced charge carrier separation

For the first time, the bio-templated porous microtubular C-doped (BTPMC) g-C 3 N 4 with tunable band structure was successfully prepared by simple thermal condensation approach using urea as precursors and kapok fibre which provides a dual function as a bio-templates and in-situ carbon dopant. Prior to the thermal condensation process, the impregnation strategies (i.e. direct wet and hydrothermal impregnation) of urea on the treated kapok fibre (t-KF) were compared to obtained well-constructed bio-templated porous microtubular C-doped g-C 3 N 4 . The details on a physicochemical characteristic of the fabricated samples were comprehensively analyze using X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Field-emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), N 2 adsorption-desorption, Thermogravimetric (TGA), and UV-vis spectroscopy. Our finding indicated that the hydrothermal impregnation strategy resulted in well-constructed microtubular structure and more carbon substitution in sp 2 -hybridized nitrogen atoms of g-C 3 N 4 as compared to the direct wet impregnation. Also, compared to pure g-C 3 N 4 , the fabricated BTPMC g-C 3 N 4 exhibited extended photoresponse from the ultraviolet (UV) to visible and near-infrared regions and narrower bandgap. The bandgap easily tuned with the increased t-KF loading in urea precursor which responsible for in-situ carbon doping. Moreover, as compared to pristine g-C 3 N 4 dramatic suppression of charge recombination of the BTPMC g-C 3 N 4 was confirmed through photoluminescence, photocurrent response, and electrochemical impedance spectroscopy. The resultants BTPMC g-C 3 N 4 possesses more stable structure, promoted charge separation, and suitable energy levels of conduction and valence bands for photocatalysis application

Concurrent growth, structural and photocatalytic properties of hybridized C, N co-doped TiO2 mixed phase over g-C3N4 nanostructured

A concurrent and facile sol-gel assisted low temperature calcination approach to homogeneous growth of TiO2 mixed phase nanoparticles over g-C3N4 for designing visible-light-driven photocatalyst is demonstrated in this study. The structural and morphological studies revealed a well-interconnected g-C3N4/TiO2 mixed phase heterojunction photocatalyst was achieved through a sol-gel process and calcination at 400 °C. The well-interconnected g-C3N4/TiO2 mixed phase heterojunction photocatalyst has strong visible light absorption capability due to the presence of an in-situ nitrogen and carbon dopants. The noticeably increased in the visible-light-photocatalytic activity performance is ascertained mainly due to the improvement of electron-hole separation and charge carrier migration

Tunable morphology and band gap alteration of CuO-ZnO nanostructures based photocathode for solar photoelectrochemical cells

A homogeneous CuO-ZnO nanostructure with tunable morphology and optical band structure is successfully synthesized via a hydrothermal method under the different dopant mole ratios of Cu. The robust correlation between the crystallite size, surface morphology, optical band gap alteration of the synthesized CuO-ZnO and its performance in photoelectrochemical (PEC) activity are investigated and compared to the reference ZnO based photocathode. In this report, it is found that the morphology of hexagonal ZnO nanorod is changed to nanosheet and vertically align CuO-ZnO based nanograss after the Cu incorporation. This result is mainly due to the composition phase change after the excessive incorporation of Cu metal into ZnO lattice. Furthermore, the optical band gap of the sample also presented a bathochromic shifted after the Cu insertion. The measurements on PEC activity of CuO-ZnO nanostructure was performed under the irradiation of a 100 mWcm−2 Xenon light in 0.5M Na2SO4 electrolyte. Among the sample, 0 Zn:1 Cu exhibited a highest photocurrent density which is 5 fold as compared to its reference ZnO samples. This finding could be due to the highest surface active area and lowest optical energy band gap in the 0 Zn:1 Cu nanograss that eventually contributes to a high free electron density that facilitates the charge transport in the photoelectrochemical cells. This novel approach could provide an alternative to the future solar hydrogenation application