Understanding the hydrogen5
Hydrogen is the first element on the periodic
table, making it the lightest element on earth.
0.00005% in air
It rises in the atmosphere and is therefore rarely
pure hydrogen gas, burning in air, producing
water and heat.
Combustion heat enables hydrogen to act as a
Colorless and odorless
Extremely reactive with oxygen and other
Low ignition energy.
High flame temperature.
Invisible flame in daylight conditions.
Small molecular size promotes leaks and diffusion.
The cryogenic liquid at 20K is even colder than
frozen nitrogen, oxygen or argon.
Key facts about Hydrogen as
Highly combustible and can be used as a fuel.
1g of combustion provides 30000 cals as compared to gasoline
gives only 11000 cals.
Can be produced from water using Biological agents.
Biologically produced hydrogen is known as Biohydrogen.
2. Steam-methane reforming process.
3. Biological process(bio-hydrogen).
Hydrogen production always requires more
energy than can be retrieved from the gas as
a fuel later on when they are produced by above
Simple setup for demonstration
of electrolysis of water.
Biological hydrogen production stands out as
an environmentally harmless process carried
out under mild operating conditions, using
Several types of microorganisms such as the
photosynthetic bacteria, cyano bacteria, algae
or fermentative bacteria are commonly utilized
for biological hydrogen production.
discovered that algae can switch
between producing O2 and H2.
1939 Hans Gaffron
1997 prof. Anastasios Malis discovered
that deprivation of
sulphur will cause the algae to switch from producing
H2.He found that enzyme hydrozenase responsible
for the reaction.
Researcher from the University of Bielfeld have
genetically changed the single cell Chlamydomonas
reinhardtiiin in such a way that it produces an large
amount of hydrogen.
2007 It was discovered that if cupper is added to
block O2 generation in algae.
2007 prof. Anastasios Malis studying solar to chemical
energy conversion efficiency in tax X mutants of
Chlamydomonas reinhardtiiin , achieved 15% efficiency .
Methods of Bio hydrogen
4.Direct Photolysis (algae)
5.Indirect Photolysis (cynobacteria)
1. Dark Fermentation
Fermentative conversion of organic substrate to
This method doesn’t require light energy.
The Gram+ve bacteria of Clostridium genus is of
great potential in biohydrogen production.
Require wet carbohydrate rich biomass as a
Produces fermentation end product as organic
acids, Co2 along with biohydrogen.
C6H12O6 + 2H2O
2CH3COOH + 4H2 +
Carbohydrate mainly glucose is preffered.
Pyruvate the product of glucose catabolism is oxidized to
acetyl-coA requires ferrodoxin reduction.
Reduced ferrodoxin is oxidized by hydrogenase which
generates ferrodoxin and release electron as a molecular
It produces valuable metabolites as a butyric acid,
It is an anaerobic process so no oxygen limitation.
It can produce carbon during day and night.
Variety of carbon sources can be used as a substrate.
Relatively lower achievable yield of H2, as a portion
of substrate is used to produce organic acids.
Anaerobes are incapable of further breakdown of
Accumulation of this acids cause a sharp drop of
culture pH and subsequent inhibition of bacterial
Product gas mixture contains Co2 which has to be
Approaches to overcome
Metabolic shift of biochemical pathway to
arrest the formation of acid and alcohol.
To improve the techniques for the seperation of
Purple non sulphur bacteria genus rhodobacter
holds significant promise for production of
Photo fermentation where light is required as a
source of energy for the production of hydrogen
by photosynthetic bacteria.
Organic acids are preferred as a substrate.
light energy required in this process is
upto the range of 400nm.
CH3COOH + 2H2 + Light 4H2 + 2Co2
Production of hydrogen by photosynthetic
bacteria takes place under illumination and in
the presence of inert and anaerobic atmosphere
for the breakdown of organic substrate to
produce hydrogen molecules.
Relatively higher achievable yield of H2, as a
portion of substrate is used to produce organic
Anaerobes are capable of further breakdown of
acids in to biohydrogen.
It can produce carbon during day only.
The combination of dark and photo fermentation
provides an integrating system for maximization of an
The idea of combined fermentation takes into an
consideration the very fact of relatively lower achievable
yield of H2 in dark fermentation.
The non utilization
Stage 1 :- Dark fermentation: Anaerobic
produces intermediates such as low molecular
weight organic acids and Co2 along with
Stage 2:- Light fermentation
The low mol wt organic acid in stage 1 are converted to hydrogen
by photosynthetic bacteria.
2CH3COOH + 4H2o
CH3COOH + 2Co2 + 4H2
Two stage fermentation can improve the
overall yield of hydrogen and overcomes the
major limitation of dark fermentation.
Drawbacks:Relatively new approach techno economic
feasibility is yet to studied
Certain green algae produces H2 under anaerobic
Under deprived of S green algae Chlamydomonas reinhardtiiin
become anaerobic in light & commence to synthesis of
Light Absorption by Photo system II (PSII) Initiates the
PSII is a large molecular complex that contains several
proteins and light-absorbing pigment molecules like
carotenoids, chlorophylls and phycobilins.
reaction center strips electrons from two water
molecules, releasing four protons and an oxygen (O2)
molecule into the thylakoid space.
electron carrier from PSII passes through the
thylakoid membrane and transfers its electrons to the
cytochrome complex, which consists of several
subunits including cytochrome f and cytochrome b6.
series of redox reactions within the complex
ultimately transfer the electrons to a second electron
carrier i.e. photo system I (PSI).
electrons are transported through the complex,
protons (H+) outside the thylakoid are carried to the
inner thylakoid space.
Light Absorption by PSI Excites Electrons and Facilitates
Electron Transfer to an Electron Acceptor Outside the
absorbed by the PSI reaction center energizes an
electron that is transferred to ferredoxin (Fd), a molecule
that carries electrons to other reaction pathways outside the
reaction center replaces the electron transferred to
ferredoxin by accepting an electron from the electron-carrier
molecule that moves between the cytochrome and the PS1
Certain Conditions, Ferredoxin can
Carry Electrons to Hydrogenase.
ferredoxin shuttles electrons to an
enzyme that reduces NADP+ to NADPH, an
important source of electrons needed to convert
CO2 to carbohydrates in the carbon-fixing
Under anaerobic conditions, hydrogenase can
accept electrons from reduced ferredoxin
molecules and use them to reduce protons to
molecular hydrogen (H2).
4H+ + ferredoxin(oxi) ――› ferredoxin(reduced)
Fig:- Schematic of Hydrogenase mediated Biophotolysis process
The US department of energy has targeted a selling price
of $2.60/kg as goal for making renewable hydrogen
1kg is approximately the energy equivalent to a gallon of
To achieve this , the efficiency of light to hydrogen
conversion must reach 10% while current efficiency is only
1% and selling price is estimated at 13.53/kg.
Hand book of bioenergy and biofuels – V K mutha
Journal on Bio hydrogen production aspotential
energy resources by Kaushik & D Das.
Bio biohydrogen – Microbiological production of
hydrogen fuel by P C Hallebeck & J R Bennemen
Bio hydrogen is fuel of future
Areas of research to increase efficiency include developing
of oxygen tolerant hydrogenase and increased hydrogen
Research on cost effective production of bio hydrogen for
commercialization is required.