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Titanium dioxide has been used as a suspension for wa-ter remediation (1) or has been immobilized on a support toallow its easy recovery to mineralize organic compounds inaqueous solutions (2). Work has been carried out with nanoc-rystalline TiO2 coatings for formic acid degradation with UVlight (3). Such coatings have also been used for the degrada-tion of humic acid (4), phenol (5), and in a clever cell thatallows the oxidation of organics at the photoanode along withthe reduction of metals, specifically copper(II), at the cath-ode (6). This latter system allowed the reduction of chemi-cal oxygen demand, COD, in aqueous solutions along withthe removal of toxic metals. Grätzel cells have used light-sen-sitized TiO2 layers on indium tin oxide (ITO) electrodes (7).Substrates for oxidation have included p-nitrophenol (8) andI− (7) or Br− (9). In the present experiment organic com-pounds are degraded at a photoanode while oxygen is reducedat a cathode of a fuel cell. An extension of the work is toimmobilize TiO2, as has been done previously (10). The useof simple composites with polymers has been carried out withzeolites (11) and mediating cobalt complexes (12).

In this experiment, an electrode coated with TiO2 is usedto oxidize organic compounds, along with an air electrodewhere oxygen reduction occurs. In addition, a tungsten lightsource is used that is safe and cheap in comparison with UVlight sources. There are a number of commercial fuel-cell kitsthat are based on a hydrogen–oxygen system (13). In addi-tion, methanol–air fuel cells have been demonstrated withprecious-metal electrodes (14), in which case a coupling ofthe degradation of organic compounds with a fuel-cell con-figuration provides an attractive environmentally friendly sys-tem. The advantages of this system are that a safe light sourceis used, there is no requirement for ITO electrodes, and theTiO2 layer can be readily cast. Students will be typically third-or fourth-year undergraduate students from environmentalscience or chemistry. Supporting lecture material on the op-eration of photovoltaic devices would be required (7).

Learning outcomes from this experiment include:• Introduction to the electrochemistry of fuel cells; a

broader discussion of the uses and limitations of fuelcells would be possible

• Introduction to the interaction between light and semi-conductors; a broader discussion of the band-gapmodel could be undertaken

• Introduction to environmental remediation andchemical analysis using HPLC

Chemicals, Equipment, and Method

Composite layers were prepared by using a suspensionof TiO2 (Degussa P25, 2.00 g L1) in tetrahydrofuran (THF)along with polyvinylchloride (PVC; 0.7 g L1) . This suspen-sion was sonicated for 10 min and typically 0.162 mL of thissuspension was measured onto a glassy carbon electrode, (3.8cm2) and dried at room temperature.

The light source was a standard 60 W tungsten spotlight, (a lamp used for recessed ceiling fittings with an inbuiltmirror that focuses the radiation, Tesco, Dublin). Glassy car-bon sheets (Tokai) and platinum foil (Goodfellow) were sil-ver epoxied to shielded copper wire and then encapsulatedwith Araldite adhesive (Radionics, Dublin). Carbon disks (3-mm diameter, Metrohm), a saturated calomel electrode(SCE), and a platinum wire formed the three-electrode one-compartment cell for voltammetry. The potentiostat was aCHI model 602 linked to a PC. Current from the fuel cellwas passed through a resistance (typically 1 kΩ) and the volt-age fed directly to a Recorderlab XYT chart recorder.

The air electrode was taken from a mini fuel cell (Electro-chem-technic, Oxford) consisting of a porous platinum elec-trode of geometric area equal to 9.6 cm2. Analysis of formicacid was carried out by HPLC as detailed in the Supplemen-tal Material.W

Hazards

Small quantities (10 mL) of the suspension in THF areprepared, which minimizes the risk since THF is flammable.The potentiostat should be operated under supervision. Theacid, H2SO4, is corrosive and appropriate precautions shouldbe taken.

Results and Discussion

In this experiment a fuel cell remediates wastewaters byoxidizing the organics and lowering the COD, while a cor-responding level of reduction happens at the other electrodewhere the substrate is molecular oxygen. A solution of for-mic acid was used to simulate wastewater. Formic acid has arapid and simple electrode reaction under the conditions usedin the fuel cell. Such simple organic acids are products of thedecomposition of organic compounds in landfills and are fre-quently found in leachates. Figure 1 shows the cyclicvoltammogram of a carbon disk modified with thePVCTiO2 composite in a three-electrode system, in ambi-

An Undergraduate Laboratory Experiment WUsing a Simple Photoassisted Fuel CellTo Remediate Simulated Wastewater

Faiza Touati and Kevin G. McGuiganDepartment of Physiology and Medical Physics, Royal College of Surgeons in Ireland, Dublin 2, Ireland

John Cassidy*School of Chemical and Pharmaceutical Sciences and FOCAS, Dublin Institute of Technology, Dublin 8, Ireland;john.cassidy@dit.ie

In the Laboratory

300 Journal of Chemical Education • Vol. 84 No. 2 February 2007 • www.JCE.DivCHED.org

ent laboratory light (A) and when exposed to light from the60 W tungsten lamp (B). It can be clearly seen that there isan enhancement of the current over a wide range of poten-tials associated with the enhanced oxidation of formic acidin solution. There is quite a similarity between the emissionof a tungsten light source and the spectral profile of sunlight(15). The cyclic voltammetry experiment is performed tocharacterize the photoactivity of the electrode. The mecha-nism of this enhancement is well-documented using UV light(8) and it is replicated in Figure 1 using a simple compositeTiO2PVC layer along with an easily accessible light source.

Figure 2 shows the photoactive behavior of a fuel cell con-sisting of a TiO2PVC composite on a carbon plate (3.8 cm2)linked to a commercial air electrode as described in the ex-perimental section. On exposure to light there is an enhance-ment of the current. The current increases from 20 µA to115 µA on exposure to the light, which is not as energetic asUV light typically used in photoelectrochemistry (3, 8, 10).This enhancement is consistent with the cyclic voltammetryresults. On exposure to light the current is constant indicat-ing a kinetically controlled system that is reversible. Oncethe cell is running, it is possible to examine the effect of theposition of the light source with respect to the electrodesalong with the relative position of the electrodes.

Figure 3 shows the decrease in the concentration of formicacid monitored chromatographically as a function of time for afuel cell with a carbon electrode (3.8 cm2) coated with theTiO2PVC composite as an anode and a Pt electrode (4 cm2)as cathode. Typically the current level changed from0.2 µA to 0.9 µA over a period of 4 hours. The concentrationdecreases linearly indicating a zeroth-order reaction as has beenfound previously for HCOOH (3). When a similar HCOOHsolution was not exposed to light, there was no decrease in for-mic acid concentration over the same period.

Conclusion

This work describes the behavior of coated electrodesusing a simple method of casting with a TiO2PVC com-posite layer. A fuel cell with this novel electrode along withan air electrode can be operated in solutions with a readilyavailable light source. This system demonstrated that evenwith low energy light sources, an enhancement of the oxida-tion efficiency is possible. This would encourage the devel-opment of systems in climates where there is continuoussunshine; obviously not Ireland! Much work has to be donefor the development of optimized cell configurations thatwould be compatible with large water masses. Most simplythe device would float on the surface of the water to employthe sun’s radiation and work is ongoing in the area.

Acknowledgment

JC acknowledges a Team Research Scheme (TERS,2004) grant from DIT. FT acknowledges funding from theGovernment of Libya.

WSupplemental Material

Instructions for the students and notes for the instruc-tor are available in this issue of JCE Online.

Figure 3. Decrease in HCOOH concentration (initial concentration= 0.1 mM) in a fuel cell consisting of a TiO2/PVC anode (3.8 cm2),and a cathode that is a Pt sheet (4 cm2) in 15 mL of solution, ex-posed continuously to 60 W tungsten lamp.

Figure 2. A current transient at a fuel cell consisting of a glassycarbon electrode coated with the composite acting as an anode(area = 3.8 cm2 ) along with a porous air electrode as cathode ina one-compartment cell with a solution of 10 mM HCOOH and0.1 M KCl on exposure to light.

Figure 1. Cyclic voltammogram for a carbon-disk electrode (area= 0.071 cm2 ) in a solution of 6 mM HCOOH in 0.1 M KCl. Athree-electrode one-compartment cell was used and potentials arequoted with respect to SCE: (A) in ambient laboratory light and (B)exposed to 60 W tungsten lamp, scan rate = 100 mV s1.

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