PMID- 28447675
OWN - NLM
STAT- PubMed-not-MEDLINE
DCOM- 20180202
LR  - 20180202
IS  - 1463-9084 (Electronic)
IS  - 1463-9076 (Linking)
VI  - 19
IP  - 19
DP  - 2017 May 17
TI  - Back-exchange: a novel approach to quantifying oxygen diffusion and surface 
      exchange in ambient atmospheres.
PG  - 12199-12205
LID - 10.1039/c7cp01317e [doi]
AB  - A novel two-step Isotopic Exchange (IE) technique has been developed to 
      investigate the influence of oxygen containing components of ambient air (such as 
      H(2)O and CO(2)) on the effective surface exchange coefficient (k*) of a common 
      mixed ionic electronic conductor material. The two step 'back-exchange' technique 
      was used to introduce a tracer diffusion profile, which was subsequently measured 
      using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The isotopic 
      fraction of oxygen in a dense sample as a function of distance from the surface, 
      before and after the second exchange step, could then be used to determine the 
      surface exchange coefficient in each atmosphere. A new analytical solution was 
      found to the diffusion equation in a semi-infinite domain with a variable surface 
      exchange boundary, for the special case where D* and k* are constant for all 
      exchange steps. This solution validated the results of a numerical, 
      Crank-Nicolson type finite-difference simulation, which was used to extract the 
      parameters from the experimental data. When modelling electrodes, D* and k* are 
      important input parameters, which significantly impact performance. In this study 
      La(0.6)Sr(0.4)Co(0.2)Fe(0.8)O(3-delta) (LSCF6428) was investigated and it was found 
      that the rate of exchange was increased by around 250% in ambient air compared to 
      high purity oxygen at the same pO(2). The three experiments performed in this 
      study were used to validate the back-exchange approach and show its utility.
FAU - Cooper, Samuel J
AU  - Cooper SJ
AUID- ORCID: 0000-0003-4055-6903
AD  - Dyson School of Design Engineering, Imperial College London, London, SW7 1NA, UK. 
      samuel.cooper@imperial.ac.uk.
FAU - Niania, Mathew
AU  - Niania M
AD  - Department of Materials, Imperial College London, London, SW7 2BP, UK.
FAU - Hoffmann, Franca
AU  - Hoffmann F
AD  - DPMMS, Centre for Mathematical Sciences, University of Cambridge, Wilberforce 
      Road, Cambridge, CB3 0WA, UK.
FAU - Kilner, John A
AU  - Kilner JA
AD  - Department of Materials, Imperial College London, London, SW7 2BP, UK.
LA  - eng
PT  - Journal Article
PL  - England
TA  - Phys Chem Chem Phys
JT  - Physical chemistry chemical physics : PCCP
JID - 100888160
EDAT- 2017/04/28 06:00
MHDA- 2017/04/28 06:01
CRDT- 2017/04/28 06:00
PHST- 2017/04/28 06:00 [pubmed]
PHST- 2017/04/28 06:01 [medline]
PHST- 2017/04/28 06:00 [entrez]
AID - 10.1039/c7cp01317e [doi]
PST - ppublish
SO  - Phys Chem Chem Phys. 2017 May 17;19(19):12199-12205. doi: 10.1039/c7cp01317e.