Biomass liquid fuel cell

The experimental results showed that the presence of more hydroxyl groups accelerated the photoelectrochemical reaction between POM and biomass, resulting in a higher degree of POM reduction, resulting in a higher power output. Therefore, biomass compounds with polyhydroxyl molecular structures such as starch, hemicellulose, cellulose, and even switchgrass and wood meal are ideal fuels for LFFC. Liu et al. used glucose as a biomass model compound to study the degradation mechanism of biomass by POM.

In fact, the POM degradation of biomass sugars by solar radiation is the result of two reactions: thermal effect and photocatalysis. Due to the strong absorption of visible and near-infrared light, the reduced POM can increase the overall temperature of the reaction system, thus significantly enhancing the oxidation of glucose. The glucose-fueled fuel cell generates electricity through photocatalytic oxidation, and at an operating voltage of 0.4 V, the battery has an energy efficiency of 36.7%, which means that consuming 1 kg of glucose will produce 1.43 kW· h of electricity.

(4) Based on non-biomass-based materials (sludge and coal)

In addition to conventional biomass, unconventional biomass fuels can also be used as fuel for LFFC, including sludge, inferior coal and grease. Sewage and sludge are hazardous wastes produced during the treatment of domestic and industrial wastewater, which contain proteins, lipids, humic acids, polysaccharides, and harmful organic and inorganic pollutants. Sludge treatment costs are high, accounting for more than 50% of the total cost of water treatment.

At present, research has reported different technical routes for treating sewage sludge to achieve energy reuse while reducing environmental impact. In the anaerobic digestion process, the sludge can be converted into biogas, liquid fuel or gaseous fuel. Two of the main technical challenges are the slow rate of methane production and the accumulation of volatile fatty acids that inhibit methane production. Sludge can also be burned directly or in conjunction with coal in coal-fired power plants, but at the same time can lead to fly ash production and toxic chemical emissions and other potential problems. Sewage and sludge power generation through MFC is an important way for municipal solid waste treatment and renewable energy development. However, due to the low power density of MFC, no practical applications have been seen so far. Zhang et al. studied the performance of sludge-based LFFC. After reacting at 100 ℃ for 24 h, most of the organic matter in the sludge was degraded. The power density of the cell can be as high as 50 mW· cm-2, which is 100 times higher than the output power of sludger-based MFC reported in the literature. Therefore, LFFC may be a promising sludge utilization method. The accumulation of soluble inorganic matter in sludge-based LFFC needs further study.

Low-quality coal (such as lignite) usually has only a lower calorific value of combustion and a lower commercial value. Therefore, there is an urgent need for technologies that can effectively utilize inferior coal and reduce environmental pollution. Weibel et al. use REDOX pair (Fe3+/Fe2+) as electrolyte to convert coal into electricity, but because the conversion efficiency is very low, the research results are not optimistic. Nunoura et al. developed an alkaline aqueous bio-carbon fuel cell that operates at high temperatures (250 ° C). However, the performance was not satisfactory and the equipment was quite complex. Zhang et al. use LFFC to obtain electricity from inferior coal without complex pretreatment. At 100~200 ℃, POM will gradually oxidize coal particles. The lignite based fuel cell has a power density of up to 120 mW· cm-2, which is the highest power density achieved by LFFC technology to date. The experimental results show that certain chemicals in low-quality coal can be converted into electricity. However, it is difficult to achieve complete oxidation and utilization of aromatic ring groups in coal by low temperature LFFC technology.

In addition to sludge and inferior coal, other types of organic matter, such as vegetable oils and animal fats, have also been used for the degradation of LFFC to generate electricity. The results show that LFFC oil treatment technology is basically impossible to achieve. There are two possible reasons for the limited degradation of oils and fats: first, the molecular bonds of oils and fats are relatively stable and difficult to crack; Secondly, the solubility of the oil in water is not very high, which increases the difficulty of contact between the catalyst and the organic matter in the water fuel cell. Liu et al. developed a system that combines anaerobic fermentation and LFFC, in which the fermentation products are used as fuel in the second step. This combined system with food residue fermentation has a high power generation efficiency (34%) and a short processing time. Since the chemicals in food residues and lignite are more complex than polyhydroxyl polymer biomass, their treatment requires the development of more efficient pretreatment methods, while new catalysts may also help improve the performance of fuel cells.