A High Power‐Density, Mediator‐Free, Microfluidic Biophotovoltaic Device for Cyanobacterial Cells

Abstract

Biophotovoltaics has emerged as a promising technology for generating renewable energy because it relies on living organisms as inexpensive, self-repairing, and readily available catalysts to produce electricity from an abundant resource: sunlight. The efficiency of biophotovoltaic cells, however, has remained significantly lower than that achievable through synthetic materials. Here, a platform is devised to harness the large power densities afforded by miniaturized geometries. To this effect, a soft-lithography approach is developed for the fabrication of microfluidic biophotovoltaic devices that do not require membranes or mediators. Synechocystis sp. PCC 6803 cells are injected and allowed to settle on the anode, permitting the physical proximity between cells and electrode required for mediator-free operation. Power densities of above 100 mW m-2 are demonstrated for a chlorophyll concentration of 100 μM under white light, which is a high value for biophotovoltaic devices without extrinsic supply of additional energy.

Polyanion‐Type Electrode Materials for Sodium‐Ion Batteries

“…In an effort to further probe the defect, diffusion, and voltage trends of the Na 4 M 3 (PO 4 ) 2 P 2 O 7 (M = Fe, Co, Ni) class of materials, a combination of atomistic energy minimization, molecular dynamics (MD), and DFT simulation techniques were carried out 75. First, atomistic energy minimization demonstrated that the Fe‐based material had the highest defect concentration, which we know has a significant impact on electrochemical performance;39 second, MD simulations suggested that the Na + diffusion coefficients and activation barriers compared favorably to those of a Li‐ion battery cathode; and third, the DFT simulation techniques demonstrated that doping Ni in Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 increased the operating potential significantly.…”

“…As compared to undoped Na 3 V 2 (PO 4 ) 3 , Mg‐doped Na 3 V 2− x Mg x (PO 4 ) 3 /C composites prepared through a simple sol–gel method exhibited obvious enhancement of the electrochemical performance in terms of both the rate capability and the cycle performance. In order to improve the efficiency of carbon coatings and to further to enhance the conductivity of the electrode material layer on the surface of carbon, Shen et al introduced the nonmetallic element nitrogen into the carbon layer 39. The nitrogen‐doped, carbon‐coated Na 3 V 2 (PO 4 ) 3 cathode material exhibited a remarkable improvement in Na storage properties, especially its rate performance.…”

“…c) The histogram for ratio of different N species in various NVP‐C‐N samples. Reproduced with permission 39. d) Schematic structure of the bonding conditions of B in a carbon lattice, B1: B4C, B2: BC3, B3: BC2O and B4: BCO2.…”

“…However, with Na 3 V 2 (PO 4 ) 3 , only Al 3+ ,36 Mg 2+ ,35 Cr 3+ ,33 N,39 and B have been reported as dopants 143. It can be rationally deduced that other transition metal and non‐metallic elements should be studied to explore their functions on other polyanion‐type compounds beyond just Na 3 V 2 (PO 4 ) 3.…”

Bioenergy Based Power Sources for Mobile Autonomous Robots

“…Use of mixed systems where photosynthetic bacteria are presented only in the cathode chamber can partly allow for reducing the illuminated area [84,85]. However, in [84], 7 mW/m 2 of power density was achieved, and, in [86], peak power density was equal to 100 mW/m 2 . Thus, the BFC with photosynthetic microorganisms is not suitable as a power supply source for autonomous robots due to its large size.…”