Artificial Photosynthesis as a Next Generation Power Source

Terms to Know Watt

Unit of power defined as one joule-second Mole

Measurement of amount of atoms/molecules in a system Joule

Unit of energy Prefix “Giga”Billion Prefix “Mega”Million Prefix “Kilo”Thousand

Photolysis Splitting by light

Photoelectrochemistry Study of light and electricity interaction with chemical substances Photoelectrochemical Cell=Photocatalytic Cell

Photocatalytic Water Splitting Splitting of water with the help of light and catalysts

Quick Facts Highest solar-to-power conversion

efficiency for a Photovoltaic Cell (Solar Panel) to date 20% Efficiency

Average amount of energy the Earth receives from the Sun per day 550 Terawatts (200 Petawatts per year)

The entire US uses 3.163 Terawatts per year The entire world uses 16.16 Terawatts per year

Photo-powered Cells vs. Petroleum Engine

Photo-powered Easily controlled reaction Very efficient energy conversion (Fuel Cell) No heat Clean Renewable Works almost limitlessly No need for refueling

Petroleum Explosive Lost energy during energy conversion (Combustion) Heat Emissions Non-renewable Needs regular refueling

Clearly Photo-powered systems are better

Quick Review of Photosynthesis Photosynthesis

6 Carbon Dioxide + 6 Water>>> Glucose+ 6 Oxygen

Requires energy Takes place in Chloroplasts of Plant Cells Light to Chemical Energy Light reactions produce Oxygen

Thylakoid Membrane Dark reactions produce Glucose

Stroma

Quick Review of Cellular Respiration Cellular Respiration

6 Oxygen + Glucose >>> ATP (Energy) + 6 Carbon Dioxide + 6 Water

Produces energy Takes place in Mitochondria of Cells Chemical to Usable Chemical Three Steps

Glycolysis: Sugar Breaking Krebs Cycle: Carbon Dioxide and ATP Production Electron Transport Chain: Water and ATP Production

Ways to Use Energy from Photosynthesis Glucose Fuel Cells

Efficient Direct Conversion of Chemical Energy to Usable Energy Provides reusable products Requires expensive catalysts (for now) such as Platinum

Cellular Respiration Efficient ATP produced will have to be converted into Usable Energy Provides reusable products Complicated to synthetically reproduce

Combustion Inefficient: Heat loss Direct conversion of Chemical Energy to Usable Energy Provides reusable products Simple reaction

Photosynthesis vs. Photocatalysis Photosynthesis

Produces Glucose and Oxygen Glucose and Oxygen combustion produces 3204 kilojoules per

mole Energy per Weight=17.8 kilojoules per gram Less weight efficient Easily found in nature

Photocatalysis Produces Hydrogen and Oxygen

Hydrogen and Oxygen combustion produces 286 kilojoules per mole

Energy per Weight=283 kilojoules per gram Very weight efficient Still being researched

Photosynthesis and electrochemistry vs. Photovoltaics

Photosynthesis/Photoelectrochemistry Convert sunlight directly to easily stored chemical

compounds Shorter Lifespan Easily adapted to current engines Still being researched technology

Photovoltaic Converts sunlight into electricity which then needs to

converted to chemical energy for storage Longer Lifespan Can not be easily adapted to current engines Well-established technology

Typical Photosynthesis Cell

Light 6(CO2)+6(H2O)

Photosynthetic Cell

C6H12O6+6(H2O)

Fuel Cell

ENERG

Y

Storage

Candidates for Artificial Photosynthesis Microalgae

Converts Carbon Dioxide and Water into Lipids at high efficiencies

Nostoc Punctiforme (Cyanobacteria) Converts Nitrogen gas into Ammonia and releases Hydrogen,

both of which can be used to create energy NAPD+/ NADPH Coenzyme System

Based off the Calvin Cycle, produces Carbohydrates which can be used to create energy

Ribulose-Bisphosphate Carboxylase (RuBisCO) Rather slow enzyme that reduces Carbon Dioxide, works in mild

conditions Blue Dimer

Catalyst based off those found in natural photosynthesis, evolves oxygen from water

Detailed Look into Blue Dimer Blue Dimer is a photocatalyst that produces

protons (H+) ions and O2 molecules from water It mimics the light reactions of Natural

Photosynthesis For it to be properly used, the Hydrogen ions

would have to be converted to H2 molecules It is much more efficient in terms of energy

production than RuBisCO systems or Microalgae To provide an even greater efficiency, the Triad

Approach could be utilized

Triad Approach

Typical Photoelectrochemical Cell

Photocatalyst

Light 2(H20)

2(H2)+O2Fuel Cell

ENERG

Y

Storage

Candidate Catalysts for Photoelectrochemical Cells Most Catalysts come from Transition Metals (D-Block) of

Periodic Table Candidates for PEC Cells are:

Vanadium Dioxide (VO2) 1.416 moles of hydrogen/gram catalyst/hour 405

kilojoules/gram/hour Sodium Tantalate (NaTaO3)

1180 millimoles/gram/hour 33 kilojoules/gram/hour Titanium Dioxide (TiO2)

180 millimoles/gram/hour 5 kilojoules/gram/hour Cadmium Compounds (Cd)

Various Rates, Highest Achieved: 14 moles/gram/hour 4 Megajoules/gram/hour

Detailed Look at VO2 System Vanadium Dioxide provides the best ratio of price to efficiency

$20 per pound 183 Megajoules per pound (Enough to power 36 houses for a day)

Vanadium Dioxide would be deposited on silicon chips via sol-gel method

Using a design similar to a solar panel, VO2 would break down a constant stream of water that would flow over it

The Hydrogen gas produced would exit via a tube at the top of the panel

Hydrogen could be stored indefinitely Hydrogen could then be catalyzed with oxygen in a fuel cell,

releasing energy Oxygen would be produced by a different catalyst, such as

Ruthenium Dioxide (RuO2)

Vanadium Dioxide Photoreactor Cell

Fuel Cell

Fuel Cell

VO2

RuO2

Basic Fuel Cell

A Final Recap Photosynthesis and Photoelectrochemistry

use light from the sun to produce chemical compounds that store energy

Stored chemical energy can be released by various methods, allowing the energy to be used

Products of the release of energy can be used to form more energy-storing compounds

Global ImpactPhotosynthetic Cells and PEC Cells, once

perfected, will provide a cheap, accessible, clean, and renewable power source. Currently the best technology is either the Blue Dimer Catalyst or the VO2 catalyst. The Photocells will help with Global Climate Change as no they will reduce CO2 emissions. Over time, once they have been incorporated into everyday infrastructure such as cars, gas stations, and power plants, they could very well make gasoline and other fossil fuels obsolete.

Other Research Metabolic Engineering

Used to modify the metabolism of organisms Research is being done into altering RuBisCO so as to make it more efficient

Fuel Cells Used to release energy from fuel Use precious and expensive metals Research being done to lower price and raise efficiency of these

Ultraviolet Upconverters Light ranges from low energy (infrared) to high energy (Ultraviolet) Most catalysts work better with higher light energies, and most sunlight

comes in lower energies UV Upconverters take photons with lower energies and convert them into a

proton with high energy Chromera Velia

Photosynthetic Protista Very good at converting sunlight into chemical energy using a different form

of RuBisCO Unfortunately, C. Velia still uses most of its produced energy

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