Photosynthetic Energy Conversion: Recent Advances and Future Perspective

Abstract

Photosynthesis is the most important natural process on earth, which transformed the once lifeless planet into a living world. While primitive photosynthetic bacteria such as purple sulfur bacteria and green sulfur bacteria carry out anoxygenic photosynthesis, producing elemental sulfur from hydrogen sulfide with the help of sunlight, cyanobacteria, algae and plants carry out oxygenic photosynthesis to convert water and carbon dioxide to sugars with the help of sunlight and release oxygen as a byproduct. The conversion of solar energy to chemical energy via photosynthesis with the release of oxygen has an evolutionary significance on life as we know it today. In fact, photosynthesis is the only natural process known on earth to form oxygen from water. Further, fossil fuels such as coal, petroleum and natural gas are formed from the remains of the dead plants by exposure to heat and pressure in the earth's crust over millions of years. With increasing energy crisis and environmental issues lately, now is the time to revisit photosynthesis in order to address these issues. In this context, a great deal of ongoing research is focused on utilizing photosynthetic energy conversion as a renewable, self-sustainable and environment friendly source of energy. When compared to the finite reserve of fossil fuels, sunlight, the energy source for photosynthesis, is abundant around the planet and is inexhaustible.The earth receives solar energy at the rate of about 120,000 TW, which far exceeds our current global demand of ~16 TW.1 However the only major technology available for solar energy conversion is photovoltaics (PV). PV devices such as solar panels generate electrical power by converting solar radiation into direct current electricity using semiconductors. Solar cells include first generation conventional wafer-based cells made up of crystalline silicon (Fig. 1a), second generation thin film solar cells (Fig. 1b)

Evaluation of Photocurrent Generation from Different Photosynthetic Organisms

“…Solar energy is the most abundant and the most exploitable sustainable energy resource. However, the technology available to convert solar energy into electrical power using photovoltaics is highly expensive and with limited efficiency due to the inherent chemical structure and composition of materials . Biological photovoltaics (BPVs), also referred to as photosynthetic microbial fuel cells (PMFC), are emerging as an energy generating technology, where photosynthetic biomaterials are used to convert solar energy into electrical energy.…”

“…Photosynthetic organisms in BPVs can reduce atmospheric CO 2 during the light independent reaction that is yet to be achieved by any of the non‐biological photovoltaics designed so far. These aspects give BPVs a greater promise over conventional photovoltaics …”

“…Cyanobacteria and algae are desirable candidates in BPVs, since they can oxidize water as the sole electron donor. Although these organisms appeared on earth from ancient time, however, they are not adapted for EET to electrodes in BPVs . Algae are eukaryotic organisms, where photosynthesis occurs in an isolated organelle, the chloroplast, into which external and extracellular redox species have limited access.…”

“…However, the technology available to convert solar energy into electrical power using photovoltaics is highly expensive and with limited efficiency due to the inherent chemical structure and composition of materials. [2] Biological photovoltaics (BPVs), [3] also referred to as photosynthetic microbial fuel cells (PMFC), [4] are emerging as an energy generating technology, where photosynthetic biomaterials are used to convert solar energy into electrical energy. In a ordinary microbial fuel cell (MFC) inorganic compounds or organic carbons acting as electrons donors are a prerequisite for function, whereas in BPVs photosynthetic organisms can use water as the sole electron donor .…”

“…These aspects give BPVs a greater promise over conventional photovoltaics. [2,5] In BPVs electrons are generated from the oxidation of water by photosynthetic materials. A variety of photosynthetic materials, e. g., isolated photosynthetic membranes [6] (thylakoid membranes), photosystems, [7] and chloroplasts [8] has been investigated in BPVs.…”