Evaluation of Selectivity and Resistance to Poisons of Commercial Hydrogen Sensors

Transcription

1 5 th Internatonal Conference of ydrogen safety (ICS) September 9-11, Brussels Belgum Evaluaton of Selectvty and esstance to Posons of Commercal ydrogen Sensors V. Palmsano *, L. Boon-Brett, C. Bonato, F. arskamp European Commsson - DG Jont esearch Centre, Insttute for Energy and Transport, Petten (NL) W.J. Buttner, M.B. Post,. Burgess, C. vkn Safety Codes & Standards Group - Transportaton and ydrogen Systems Center * valero.palmsano@ec.europa.eu Natonal enewable Energy Laboratory, Golden CO 841

2 Insttute for Energy and Transport Part of the Jont esearch Centre (JC),.e. the European Commsson s n-house scence servce. JC-IET Msson: to provde support to Communty polces and technology nnovaton n the feld of 1) energy - to ensure sustanable, safe, secure and effcent energy producton, dstrbuton and use 2) transport - to foster sustanable and effcent moblty n Europe. Independent of prvate, natonal, fnancal or commercal nterests Cooperaton wth leadng scentfc organsatons n the Member States, Assocated Countres and worldwde.

3 JC- sensor testng faclty (SENTEF) Performance testng of 2 Safety Sensors Comparson of dfferent sensng technologes Influence of ambent parameters/contamnants Sensor response/recovery tme measurement chamber Temperature: -4 C +13 C Pressure: 1 25 kpa : -4 C, 6 C 4 MFCs for nlet gases ( 2, CO, C 4, CO 2, SO 2, ) GC Gas analyss GC collaboratons L. Boon-Brett, J. Bousek, P. Castello, O. Salyk, F. arskamp, L. Aldea, F. Tnaut, IJE, Volume 33,

4 Mature technologes for sensng 2 Thermal Conductvty (TCD) Catalytc (CAT) Semconductve Metal-Oxde (MOX) Electro-chemcal (EC) Metal Oxde semconductor (MOS) Pd Thn Flm (PTF) 2 : hghest thermal conductvty of all known gases. [ 2 ] T at sensng pont, detected through a Wheatstone brdge. A sensng element detects the heat of combuston of 2 wth O 2 at the Pd/Pt catalyst. ydrogen gas reacts wth chemsorbed O 2 n a semconductng materal, such as tn oxde, and changes the resstance of the materal. Oxdaton of 2 at the sensng electrode producng a current proportonal to [ 2 ]. Counter reacton at the cathode (reducton of O 2 ) 3 layers structure: metal-nsulator (oxde)-semconductor. 2 splt at catalytc metal (Pd) gvng rase to a -dpole layer (at the nterface) work functon changes Most common relate the resstance of a Pd-based thn flm to the external concentraton of 2 Developpng technques: Optcal, acustc, mechancal

5 Cross senstvty / posons ssue Cross-senstvty (.e. selectvty): ablty of a sensor to respond to the target analyte, regardless of the presence of other speces. Cross-senstvty and resstance to posons are consdered man ssues by sensor end-users because can lead to: Undetected hydrogen leaks, wth serous safety consequences False alarms, wth economc damage (false negatve) (false postve) We use ISO as a gude to defne the effect of: Interferents, transent effect on the sensor performances; Posons, the effect persst after exposure.

6 Strateges for selectvty TCD CAT MOX EC MOS espondng to any speces wth a thermal conductvty dfferent than ar. Practcally only e and few other speces at hgh concentraton. No poson effect expected (no chemcal reacton s nvolved ) In prncple may respond to any combustble gases. Selectvty: Pd catalyst + flters/ molecular seve coatngs. Poor selectvty to 2,.e. respondng to CO, C 4, 2 O. Varous strateges to ncrease selectvty: adjustng the MOX crystal structure and composton wth dopants; optmsng the sensng materal operatng temperature for 2 detecton; coverng the surface wth a slca layer. Membranes, (hnderng dffuson of gasses 2 nto the electrode); Selectve materals (for 2 ) catalysng the electrochemcal reactons. Selectvty assured by the use of specfc catalytc metals (Pt, Pd). PTF Pd surface selectve to 2 ; Protectve membranes (e.g. polymers lke PTFE) aganst posons (CO, SO 2, 2 S and S-based compounds).

7 Exposure profle a) Exposure to 1vol% 2 n ar (control measurement stage) b) Exposure to 1vol% 2 n presence of the nterferent "" (cross-senstvty measurement stage) c) Exposure to 1vol% 2 n ar (recovery stage / poson effects) The dluent gas s clean ar. Exposure profle for the cross senstvty test.

8 Exposure profle Gas speces "" and test concentratons Speces "" c [ppm] CO 2 5 level allowed by US OSA C 4 1 2% LEL CO 5 level allowed by US OSA Exposure profle for the cross senstvty test. SO 2 5 ISO standard The response to other speces s beng tested.

9 EC platform vs. C 4 a) eference (a) (b) (c) b) Cross senstvty effect c) Poson effect No effect!

10 EC platform vs. SO 2 Net response to the nterferent X = =.6,, 3hrs Increment of the senstvty to 2 n presence of the nterferent X =, 1 =.3 Change n the baselne after 3h exposure P P,3hrs = = =,3hrs Increment of the senstvty to 2 (post-exposure) 1 =.6,3hrs

11 Catalytc platform Cross senstve to SO 2 Speces X X 5 ppm SO ±.5.5 ±.5 5 ppm SO 2 : detrmental on the sensor output. Partally recovered by exposure to clean ar Speces P P CAT response durng the exposure profle wth 5 ppm SO 2 5 ppm SO ±.5 -.5±.5

12 MOX platform Neglgble effect of CO and CO 2 Cross senstve to C 4 : promoter for the absolute response; nhbtor for the net response. Speces X X 1% C 4.65 ± ±.1 MOX response durng the exposure profle wth 1. vol% methane.

13 TC platform No poson effect was found. Neglgble X for any gas tested. K C4 >K ar X > K CO2 <K ar X < Speces X X 1% C 4.14 ± ±.2 TCD response durng the exposure profle wth 1. vol% methane.5% CO ±.2 -. ±.5

14 Expensve platforms: PTF, MOS Table of results Speces PTF MOS.5% CO 2!!!!!! 1% C 4!!!!!! 5 ppm CO!!!!!! 5 ppm SO 2!!!!!!

15 Summary of results Speces PTF MOS EC TCD MOX CAT.5% CO 2 Interferent To be tested 1% C 4 Interferent Interferent Interferent 5 ppm CO 5 ppm SO 2 Interferent POISON To be tested Interferent POISON

16 Conclusons and outlook Expensve technologes (MOSFET, PTF) shows hgh selectvty to 2 no poson effects,.e. the sensors are well protected. EC s posoned by SO 2. TCD shows cross senstvty to CO 2 and to C 4. No poson effect found. Inexpensve technologes (CAT, MOX) shows hgh cross senstvty to C 4 and poson effects (SO 2 ),.e. the sensors are not specfc to 2. The effect of other gas speces to be consdered: N 3 ; 2 ; 2 S MDS (N-based compounds) (S-based compounds) (S-based compounds)

17 Aknowledgements JC-IET s supported through European Commsson s 7 th Framework Programme The NEL Sensor Laboratory s support by DOE- EEE Fuel Cell Technologes Offce. * valero.palmsano@ec.europa.eu 17

18

19 Extra slde: TCD X ~ c ~ K = proportonal ( K K ) Ar ; c = 1% = Ar c c % CO2 :.5 =.3 = % C 4 : = K Ar K K 2 K K Ar Ar = Gas Speces Thermal Conductvty K [mw/(m.k)] K / K Ar Ar ydrogen, elum, e Carbon Doxde, CO Methane, C Carbon Monoxde, CO Expermental X (.5% CO 2 ) -.3 ±.2 (agreement wth calculatons) Expermental X (1% C 4 ).14 ±.2 (3 tmes the expected value) Thermal conductvty of varous gas speces "".

20 EC platform vs. SO 2 Net response to the nterferent? X = =.6,, 3hrs Influence the senstvty to 2?, X = 1 =.3 Does t recovers (3h exposure)? P,3hrs = = Senstvty to 2 (after 3h exposure)? P =,3hrs 1 =.6,3hrs

21 CAT platform Neglgble effect of CO and CO 2 Cross senstve to C 4 : promoter for the absolute response; nhbtor for the net response. Not a poson. Speces X X 1% C 4.66± ±.2 CAT response durng the exposure profle wth.5 vol% methane.