Solid-state amperometric hydrogen sensor based on polymer electrolyte membrane fuel cell

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<ul><li><p>Sensors and Actuators B 107 (2005) 812817</p><p>Solid-state amperometric hydrogebra</p><p>Wany of ChHefei, Aber 20</p><p>Abstract</p><p>An amper The se(PEMFC) us te (SPEgas-diffusio fixed pstate current ,500 pthe sensor a or preplinear range and long-term stability. It can be used to monitor hydrogen concentrations in gas mixtures on-line. If the sensor is improved toachieve a lower detection limit, it may be applied to detect hydrogen in aqueous solution. 2004 Elsevier B.V. All rights reserved.</p><p>Keywords: Gas sensor; Amperometric hydrogen sensor; Polymer electrolyte membrane fuel cell; Gas-diffusion electrode</p><p>1. Introdu</p><p>Hydrogularly in pelead to exptems oftenrosion [2,3drogen evoevolved, threleased caational safeto ensure thsystems [1gen sensor</p><p>Amongdrogen sentheir pecul</p><p> CorresponE-mail ad</p><p>0925-4005/$doi:10.1016/jction</p><p>en is an important industrial raw material partic-trochemistry and energy sources. Its leakage canlosion and its penetration in metal and alloy sys-results in hydrogen embrittlement [1]. Metal cor-] often occurs via mechanisms that involve hy-lution. By measuring the amount of hydrogene kinetics of many reactions where hydrogen isn be studied. The industrial importance and oper-ty of hydrogen demand reliable hydrogen sensorse effectiveness of the process and hazards control</p><p>]. These all accelerate the development of hydro-s.</p><p>a variety of hydrogen sensors, electrochemical hy-sors [47] receive more and more concerns foriar merits. Electrochemical hydrogen sensors, in-</p><p>ding author. Tel.: +86 551 3606229; fax: +86 551 3601594.dress: (S. Wu).</p><p>clude potentiometric [8,9] and amperometric [10,11] devices.Potentiometric sensors have a wide dynamic range but lack ofaccuracy for their logarithmic response. Amperometric sen-sors are linear in their response and are more accurate. Com-pared with liquid electrolytes, solid polymer electrolytes havethe advantages against the possibility of leakage, corrosionand volatilization. Amperometric hydrogen sensors based onSPE are smaller in dimension and lighter in weight, thus al-lowing miniaturization. Nafion (Dupont, USA) as one of thebest proton conductors, has been widely used in fuel cells andelectrochemical gas sensors. Gas-diffusion electrodes havebeen developed with the progress of fuel cell technology.They have high efficient three-phase boundaries where thereacting gas, metallic electrode and electrolyte meet togetherand react.</p><p>Several attempts have been made to develop solid-statehydrogen sensor operative at ambient temperature. For ex-ample, Liu and coworkers [12] have reported a solid-stateamperometric detector for sensing hydrogen on a Pt/C/Nafioncomposite electrode prepared by mechanically hot-pressing</p><p> see front matter 2004 Elsevier B.V. All rights reserved..snb.2004.12.022polymer electrolyte memXianbo Lua, Shouguo Wua,, Li</p><p>a Department of Chemistry, University of Science and Technologb Anhui Electric Power Test and Research Institute,</p><p>Received 29 June 2004; received in revised form 29 Novem</p><p>ometric hydrogen sensor of whole solid-state has been Nafion membrane as proton-conducting solid polymer electroly</p><p>n electrodes. The sensor can work at ambient temperature. When as respond linearly to the concentrations of hydrogen from 560 to 11re investigated and discussed. The simple miniature hydrogen sensn sensor based onne fuel cell</p><p>ga, Zhenxi Sub</p><p>ina, Hefei, Anhui 230026, PR Chinanhui 230026, PR China</p><p>04; accepted 9 December 2004</p><p>nsor based on polymer electrolyte membrane fuel cell). It adopts three-electrode mode that consists of three</p><p>otential of 0.15 V is imposed on the sensor, the steady-pm (v/v). The factors that influence the performance ofared shows good sensitivity, short response time, wide</p></li><li><p>X. Lu et al. / Sensors and Actuators B 107 (2005) 812817 813</p><p>a Pt/C film onto one side of Nafion. However, the hydrogensensor reported still needs 1 M H2SO4 as liquid electrolyteand a saturated Ag/AgCl electrode as the reference electrode.The directtion is alwatypes of seat high tembut whichistent. Theprovide a redirectly to</p><p>This papa new ampIt used a Nroethylenebrane. Theemployingform threetrodes witha counter ereference eresponse bare discuss</p><p>2. Experim</p><p>The Na1 h to remo0.5 mol/l Hties and to ewith distillwater.</p><p>The carbcommerciaFraga et aH2PtCl6 soof about 30the pH of t5 mol/l NaOthe H2PtCltate (Pt/C)washed wi383 K overcohol, Nafision (60 wtto their weiture was us</p><p>A Fig. 1.</p><p>The sensdures. Firstmembraneof the mixt</p><p>Schem(2) Pt/RPt/C ca(6) refe</p><p>the thd withthe t</p><p>ce are</p><p>placeively.C andiame</p><p>mm.</p><p>e schwn inconstaas mi</p><p>in nitr0 ml/</p><p>7A/ZMitioned) untiases wd NaCThethe c</p><p>sed tomicroII, LAmper</p><p>ata weow ra</p><p>esults</p><p>Princi</p><p>e elecn of h</p><p>2H+</p><p>he red</p><p>+ 2H+ + 2e H2O (2)he sensor has a Pt(C)|air reference electrode.e sensor response current is controlled by the diffusionf bulk hydrogen or the oxidation rate of hydrogen. Whenxidation rate of hydrogen is much higher than the diffu-rate of bulk concentration, the electrochemical reactionsdetection of dissolved hydrogen in aqueous solu-ys a challenge for electrochemical sensor. Some</p><p>nsors for monitoring dissolved hydrogen in waterperatures (T&gt; 200 C) have been reported [13,14],can be used at ambient temperature is still inex-unique structure of the sensor we designed canference for constructing a sensor that can be used</p><p>detect hydrogen in aqueous describes the configuration and fabrication oferometric hydrogen sensor of whole solid-state.afion-117 membrane as SPE, and a polytetrafluo-(PTFE) sheet as a gas-permeable diffusion mem-sensor was based on a three-electrode system,platinum supported on carbon as a catalyst togas-diffusion electrodes. Among them, two elec-large surface area act as a working electrode andlectrode, respectively. Another acts as Pt(C)|airlectrode. The basic principle, assembly details,ehavior and application of the hydrogen sensored.</p><p>ental</p><p>fion-117 membrane was boiled in 5% H2O2 forve organic impurities. Then it was immersed in2SO4 at 80 C for 2 h to remove inorganic impuri-xchange ion for H+ completely. After being rinseded water, the membrane was stored in deionized</p><p>on-supported platinum catalyst was prepared. Al activated carbon was pretreated according tol. [15]. Then it was impregnated with aqueouslution of 4 mg/ml to obtain a nominal Pt loading%. After the solution was stirred for half-an-hour,he impregnation solution was adjusted to 13 with</p><p>H, then 33% formaldehyde was added to reduce6 completely. After 12 h of stirring, the precipi-was obtained by filtration. The Pt/C catalyst wasth distilled water and dried in a vacuum oven atnight. Then Pt/C, distilled water, anhydrous al-on emulsion (5 wt.%, Dupont) and PTFE emul-.%, FR301B, China) were well mixed accordingght ratio of 10:3:10:3:3. Finally, the obtained mix-ed as the catalyst layer of the sensor.oporous PTFE membrane was used as a gas-diffusion membrane, and Pt/Ru meshes as currentThe structure of the sensor is schematically shown</p><p>or was prepared according to the following proce-of all, the Pt/Ru mesh was placed onto the PTFEand its upper side was coated with a thin layerure. Then the Nafion-117 membrane was placed</p><p>Fig. 1.brane;trode (trode;</p><p>ontocoatewhilesurfawere</p><p>spect110 The d15</p><p>This sho</p><p>AThe ggen (at a 6D07-condargontest gurate76%.whileexpoing aLK98ent tethe dgas fl</p><p>3. R</p><p>3.1.</p><p>Thdatio</p><p>H2and t12 O2</p><p>and tTh</p><p>rate othe osionatic diagram of the hydrogen sensor structure. (1) PTFE mem-u mesh (embedded into the catalyst layer); (3) working elec-</p><p>talyst thin layer); (4) Nafion-117 membrane; (5) counter elec-rence electrode; (7) insulator.</p><p>in layer and the other side of the membrane wasa thin layer of the mixture immediately, mean-</p><p>hin layer was divided into two parts of differentas by an insulator. Afterward, two Pt/Ru meshesd onto the two divided parts of the thin layer, re-Finally, the assembly was placed in a hot-press atkept for 10 min under the pressure of 40 kg/cm2.</p><p>ter of the sensor with 3.0 mg/cm2 Pt loading was</p><p>ematic diagram of the assembled hydrogen sensorFig. 2.nt potential of 0.15 V was imposed on the sensor.xtures containing known concentration of hydro-ogen or in air) were introduced into the chambermin flow rate controlled by a flowmeter (model:</p><p>, China). Before measuring, the sensor was pre-by passing the humid carrier gases (nitrogen or</p><p>l the output signals reached steady values. Theere moisturized by passing them through a sat-l solution, ensuring a relative humidity (RH) ofworking electrode was exposed to the test gas,ounter electrode and the reference electrode werethe air. The measurements were carried out us-</p><p>computer-based electrochemical analyzer (model:NLIKE, China) interfaced to a computer at ambi-</p><p>ature of 25 2 C. Without special statement, allre obtained with 1# hydrogen sensor at 60 ml/minte and 76% RH.</p><p>and discussion</p><p>ples of the sensor</p><p>trochemical processes taking place are: the oxi-ydrogen at the working electrode</p><p>+ 2e (1)uction of oxygen at the counter electrode</p></li><li><p>814 X. Lu et al. / Sensors and Actuators B 107 (2005) 812817</p><p>Fig lectrod</p><p>are a diffuson fuel cellternal poweon the hydroxidation oside reactiocan catalyzization potthat when asensor, theand the linetion potentbring the inCO, SO2, eand the lowof the hydr</p><p>The sensidered to bstudy the P0.1m apediffusion blength in telectrode cture. The Pof the gas bcontrolled</p><p>Under tpressed as</p><p>il = KCb</p><p>e Cbhe sennds onthe amf themiting. 2. Schematic diagram of the assembled hydrogen sensor. (WE) Working e</p><p>ion-limited process. The hydrogen sensor basedprinciple can operate without the need for an ex-r source. When a polarization potential is imposedogen sensor, on the one hand, it can accelerate thef hydrogen; on the other hand, it may cause somens because the Pt/C is a high efficient catalyst that</p><p>wherand tdepearea,</p><p>etc. Ithe lie many chemical reactions. Therefore, the polar-ential should be suitable. In our study, we found</p><p>constant potential of 0.15 V was imposed on thesteady-state response currents were very steadyar range was wider than that without the polariza-</p><p>ial. Meanwhile, the polarization potential will notterference of other gas that may coexist, such astc. Both the conductivity based on hydrogen ionpolarization potential contribute to the selectivity</p><p>ogen sensor.sing mechanism of the present sensor can be con-e similar to that reported [16]. Differently, in ourTFE membrane with numerous micropores aboutrture was used instead of a capillary hole-typearrier about 0.150.85 mm diameter and 20mmhat paper. It simplifies the structure of sensing-hamber compared with that reported in the litera-TFE membrane micropores can restrict the accesseing measured and thus ensure it is a gas-diffusion-process.his condition, the limiting current il can be ex-follows:</p><p>(3)</p><p>hydrogen.</p><p>3.2. Measu</p><p>There arhydrogen, itest gas andreactions aflow rate wthe resultinrate versus11,500 ppmincrease stethey increaconstant flo</p><p>The PTin limitingpropriate Pand thickneear range othe calibratPTFE diffuwith a 0.20.0265Ae; (RE) reference electrode; (CE) counter electrode.</p><p>and K stands for the concentration of hydrogensitivity of the sensor, respectively. The value of Kmany parameters, such as the effective electrodebient temperature, the diffusion rate of hydrogen,parameters are invariable, K is a constant, andcurrent il is proportional to the concentration ofrements of the sensore several factors that influence the diffusion rate ofncluding the diffusion coefficient, the flow rate ofthe diffusion barrier. Because the electrochemical</p><p>re a diffusion-limited process, the hydrogen gasill influence the diffusion rate of hydrogen andg response signal. Fig. 3 is the plot of gas flowresponse signal for the sensor in the presence ofhydrogen. It can be seen that the response signalseply before the flow rates reach 40 ml/min, then</p><p>se steadily. In our study, we select 60 ml/min as aw rate, which is near the plateau.</p><p>FE diffusion membrane plays an important rolethe diffusion rate of hydrogen. By selecting ap-TFE diffusion membranes with different aperturess, we can control the sensitivity and (or) the lin-f the hydrogen sensor to some extent. Fig. 4 ision curves for the sensors with different aperturesion membranes. The sensitivity of the sensor (2#)m aperture PTFE diffusion membrane is about/ppm, which is about two times larger than that of</p></li><li><p>X. Lu et al. / Sensors and Actuators B 107 (2005) 812817 815</p><p>Fig. 3. The plot of H2 gas flow rate vs. response signal for the sensor in thepresence of 11,500 ppm hydrogen.</p><p>the sensor (1#) with 0.1m aperture PTFE diffusion mem-brane (0.0103A/ppm).</p><p>Another important factor that influences the response sig-nal is the relative humidity of the gas mixture. Since theproton-condepends onsary to keepWe tested tcertain RH42% (saturNaH2PO4 sa strong im</p><p>Typicalcentrations</p><p>Fig. 4. The cadiffusion mem</p><p>Table 1The sensitivities of 2# sensor at different relative humidities</p><p>Relative humidity (%) Sensitivity (A/ppm)42 0.01776 0.02695 0.031</p><p>Respo</p><p>, theme. Its mixentratie steade caligen concentrations is demonstrated in Fig. 6. According. 6, the linear regression equation is y= 3.14 + 0.0103x,ductivity of the Nafion-117 membrane stronglythe water content in the membrane, it is neces-the relative humidity (RH) of test gases constant.</p><p>he 2# sensor in the range of 101611,500 ppm at a. Table 1 shows the sensitivities we obtained at RHated Zn(NO3)2 solution), 76% and 95% (saturatedolution). The relative humidity of the test gas haspact on the sensitivity of the sensor.current-responses of the sensor to various con-of hydrogen are illustrated in Fig. 5. As shown in</p><p>Fig. 5.</p><p>Fig. 5ery tiin gaconc</p><p>of thTh</p><p>hydroto Figlibration curves for the sensors with different aperture PTFEbranes.</p><p>Fig. 6. The cagen.nse curves of the sensor for various concentrations of hydrogen.</p><p>sensor has stable sensing current and good recov-can be used to monitor hydrogen concentrations</p><p>tures on-line. On a step change of the hydrogenon, the response time (time required to reach 90%y-state current) of the sensor is about 2050 s.bration plot of steady-currents of the sensor versuslibration plot of steady-currents vs. concentrations of hydro-</p></li><li><p>816 X. Lu et al. / Sensors and Actuators B 107 (2005) 812817</p><p>where y and x stands for the response currents (A) of thesensor and the concentrations (ppm) of hydrogen, respec-tively. The sensitivity of the sensor is 0.0103A/ppm, whichis about 10RH (76%)11,500 ppmFor exampsensor withcover gas.the range ocan be wid</p><p>Compar[16,17], thethe same ccan be attriThe electroon the threeelectrolytethe effectivon the elecalyst layercarbon-supalyst prepahas high cadiffusion egas-diffusierated in thgas-diffusioxidized atthe porouscatalyst layelectrodesconductivitcatalyst layconsistingon our expdiffusion enents are vsensitivitythe water ctrodes is rehydrophobcontent in t</p><p>It shoulcentrationgen concenby the reachence theof the sensin nonlineagen concenof steady-c(11,50010sitivity) inclinearity deto the incre</p><p>. The calibration plot of steady-currents vs. high concentrations ofgen....</p></li></ul>


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