CHUEH Will  Energy Conversion Limits 4 Feb 2013

Energy conversion... where and when needed

Solar conversion to batteries or hydrocarbon or hydrogen storage

then delivery then utilize...

H2 is hard to store or can store as  methane

electrochem conversion... fuel cell or water splittng cell or battery etc

ChuehLab. stanford

theme today: material optimization and discovery...

he shows a nano-column Sm-doped CeO2  device...

sensitivity  ppb
timescale  psec to femtosec
spatial res at angstrom level
as electrochem takes place

SSRL  synchrotron light source  SSRL

and ALS at LBNL  and SNC  stanford nanotech center...

topic 1 ... batteries...

sunlight water and CO2 to charge a battery...

want to incr  energy density of battery  but also
power density... how fast can u discharge it  in watts per kgm

energy density in  watt, hours per kgm

power density:  fuel cell worse  then conventional battery then  ultracapacitor....

understanding battery charging and discharging

A123  (now defunct)  look at it at 500nm...  indiv particles  they all interact with one another

A123 used  Li FePO4  went from lots of litium to no lithium at 0 volts  as it discharged.

profound impact on charging and charging...

lithium is the energy carrier...

we want to SEE lithium move inside battery  they
work with ALS at LBNL and coherent light source to see it...

lithium changes iron oxidation state  (from 2+ to 3+) as li is removed...

LiFePO4 looks vidfferent than FePO4... so can get a lithium map...
particles are abt 30 to 500 nm...

where did lithium go

can see it with  TEM and with  charge mapping vis  STXM

see that it is heterogeneoous...

so they charge concurrently or sequentially...

he can say exactly how many are charged, discharged, or mixed...

many are either red or green...  only tow particle were mixed in this field of about 5 micron by 5 micron.

only 2% were actively being charge....

98%  of particles were doing nothing!!! during charging or discharging...

so,  it is  really SEQUENTIAL  (like popcorn popping)

why can they be chared so rapidly eg in 1 to 2 mins for a single particle...

green = charged; red = discharged;

106 nm particle prob of being charged = 80%

and 321 nm  prob was stilla bt 50%...

resolving  the battery into individual particle batteries...

so how to improve rate capability...

is it propagation limited  or
initiation limited?  (may need a bit of time to get ready to pop... like popcorn)

so, do u want particles to be really small or doe it not matter?

now, want to record image of battery  while its being charged  (a movie, not a still image)
with a res of 30 nm...

look at boeing  787 batt. fiasco... hwo did it fail?

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topic 2:  fuel cells...

hydrogen or methane... turn it into electricity  (with H2O as byproduct)

over depends on precious materials  (like platinum)

1 gram of platinum for every  kiloton of sand...

93% of platin. is imported; 80% is in S aftrica  (world reserves)

so,  must eliminate use of platinum, etc.

membrane:  air on one side;  fuel on other;

catalytic combustion of fuel with oxygen...

left:  GM  fuel cell  (at 80 degr celsium)

Bloom Box... solid oxide  (at 800 degr celsius...) for stationary apps.

GM  works at 80 degr C;  cheap, reliable,  uses steel...

the Bloom box is also good;  at 800 degr C... no prec metals...

can we combine these features to get something tahat works at 400 to 600 degr celsius...

eliminate metal altogether...

anode... free of precious metal...

bulk properties do not matter...
what matters is the surface...

so look in-situ  for  active sites...

use synchrotr rad at SLAC and at LBNL...

fuel cell... must have  oxygen....

can use  enviro  TEM   resol is subnanometer...
enviro transmission electron microscop...

can run at  2% of atmosphere...

can also use surface xray scatering...

start with Bloom Box... how to stick it into   sychro light source....

turn it into a chip that is 1 by 1 cm....

built on single xtal...

how is charge xfer in a fuel cell trode?

what is rate limiting step?

slowest step is xfer of electrons...

convert hydrogen to water on cerium oxide surface...

its the single electron xfer from hydrogen to oxide  that is rate limiting..

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can we convert water into  hydrogen...   water splitting...

start with water and split to hydrog and O2...

effic is 5 to 10%.

room temp is not the best...

reac rate goes much fater at high temp....

optimal temp is prob   200 celsius...

but ... move drak current to r...  lessen it  (dark current...  charges moving in wrong direciton)

go to solid cell rather than liquid...

he shows band gap  (what photons can be absorbed)... want 1.2 eV traditionally... but effic is almost zero there...

best is  abt 1.6  eVolts

but can incr temp to 800 degr  and do ot have to use  precious metal...
operate at 2 eV...

focus sunlight using giant mirrors...  cocentrating solar power...

replace steam  ...

iron oxide has a 2 eV bandgap !!!!   

want ot get effic of 15 to 30%  (also convert thermal energy)

building a proof of concept prototype...

Take home msg:

fundamental insights  are key...

lead to unexpected ways to improve perfomance...