Build Your Own Working Model

Ion-Exchange Fuel Cellthe futureproject

Hydrogen and oxygen produced by electrolysis react in the fuel cell to create electricity. In practice a motorcould be temporarily reversed to generate current for electrolysis, eliminating batteries.

in it, and attempts arebeing made to buildfuel cells which willproduce enough powerper unit volume tomake them practical.

Basically, a fuel cellis an electrochemicaldevice for conversionof chemical energy in-to electrical energy.The principle of opera-tion is generally thesame as an ordinaryflashlight or automo-

bile battery, except that the fuel and oxidantare supplied from outside of the cell whileit is operating.

You can build a fuel cell and a hydrogen-oxygen generator (Fig. 1) from about $10worth of materials that will demonstrate thisprinciple and serve as a model for futureexperiments. Remember that the fuel cell isnot a toy, but a device with tremendous po-tential for experimental improvement. Assuch, it involves working with hydrogen,oxygen and corrosive solutions. These de-mand use of ordinary laboratory precautions,such as careful handling of the liquids andavoidance of open flames in the area whilehydrogen is being produced or used.

Make the Fuel-Cell Casing from two 1/8 x

One of these power supply units ofmakes an excellent science fair

By ELTON J. CAIRNS

AT ITS present stage of development, thefuel cell is a highly efficient, compactpower unit that produces no toxic ex-

haust fumes, high temperatures, high pres-sures or noise. In special cases, it can beused to manufacture its own fuel and oxi-dant; usually hydrogen and oxygen.

Since these attributes are just those beingsought in power plants for long-distance sub-marines and space ships, it is not surprisingthat the fuel cell has attracted the attentionof today's engineers and scientists.

The fuel cell itself is not a new concept;the first one was constructed in 1839 by W.R. Grove. Now, however, the growing de-mand for a power plant with the characteris-tics of the fuel cell has created new interest

106 SCIENCE AND MECHANICS

3-1/8"x3-1/8" pieces ofplastic. Lay out theeight 1/8-in. holes (Fig.2A) and tape thepieces together, drill-ing through bothsheets at the sametime. Temporarily in-sert three or four boltsand saw the 3-in. dia.casing from the sheets.Using one of the cellcasings as a template,lay out the six boltholes on two pieces of1/16-in. rubber gasketmaterial. Punch theholes and cut a l-1/2in.opening (Fig. 2B) inthe center of each gas-ket. Save six of the1/8-in. slugs punchedfrom the gaskets to beused as spacers whenassembling the casing.

Cut the electrodes(Fig. 2C) from 100-150mesh nickel screen,providing 1/4xl-in.tabs to be used as ter-minals. The nickelelectrodes are given acoating of -platinum-black which serves asa catalyst to speed upthe reaction of hydro-gen and oxygen atroom temperatures.Remove all grease andoil from the screenswith dry cleaningfluid, dry them thor-oughly, and placethem in a 5% platinicchloride solution untilthey have becomeblackened (about 20minutes). Take themfrom the solution witha tweezers, rinse withwater and dry be-tween blotters.

Cut a 2-in. disc froma sheet of anion ex-change resin or What-man #50 filter paper.This disc will serve to store the electrolyteand must be soaked in it before assembly.The electrolyte is made of 30 grams of potas-sium hydroxide in 100 cc of water. Add thehydroxide to the water slowly to preventdangerous overheating. Handle the solutioncarefully as it is harmful to your skin andhighly corrosive on material other than plas-tic, rubber or glass. When the disc has ab-

sorbed as much of the electrolyte as possible,take it from the solution and remove the ex-cess liquid with a blotter, leaving the discdamp, but not wet.

To Assemble the Cell (Fig. 3), place a gas-ket and three of the spacers on one of the cas-ing-halves. Place one of the electrodes ontop of the plugs with the tab extending be-yond the edge of the case. Cover the elec-

DECEMBER, 1960 107

r

1/2 x 5 x 12-in. board to which you have at-tached a miniature toggle switch with four6-in. leads and alligator clips. Drill holes inthe board in which the cell and test loads,such as a motor, lights or a meter, can beplaced. Mount the cell by bending a stiffcopper wire around the ends of the screwsand forming a leg to fit in the test stand(Fig. 3).

A Generator to manufacture oxygen andhydrogen is made by using an electrolysissetup (Fig. 4) with potassium hydroxide asthe electrolyte and nickel screens as elec-trodes. Fill a 5in. deep pyrex pan 3/4 full of

a 10% solution of potassium hy-droxide (1/2 lb. of hydroxide to 1/2gallon water). Fill two small bot-tles with the solution and placethem upside down in a support inthe liquid with no air in the bot-tles. Clamp one end of two 3-ft.pieces of 1/8-in. plastic tubing andplace the other ends well up intoeach of the bottles. Connect two3-ft. insulated copper wires to 1 x2-in. nickel screen electrodes andplace one of the electrodes just

R u b b e r r e s p i r a t o r b a g s f i l l e d w i t h p u r c h a s e d h y d r o g e n a n d o x y g e nr u n A r i s f o - R e v m i d g e t m o t o r a n d 6 - i n . p r o p e l l e r f o r s e v e r a l h o u r s .

trode with the disc containing the electrolyteand place the second electrode on this. Besure the electrodes do not touch each otherby arranging the tabs so one is on each sideof the vent ports. Now place the remaininggasket, spacers, and casing-half on top, lineup the bolt holes and ports, and fasten thecell together with 10-32 x 3/4-in. bolts andnuts. Do not fasten the nuts so tightly as toforce the gasket beyond the edge of the case.Glue 1/8-in. o.d. metal or rigid plastic pipes inthe intake and vent ports so the feed tubescan be slipped over them.

Now make a testing stand (Fig. 1) from a

108 SCIENCE AND MECHANICS

inside of the mouth of each bottle.Then connect the wire to two orthree 1.5V series wired, dry cells.Gas will immediately begin to col-lect in the bottles; hydrogen at thenegative electrode and oxygen atthe positive. (Caution: hydrogenis combustible. Keep flame awaywhile the generator is operating.)Allow gas to collect until the oxy-gen, which is generated only halfas fast as the hydrogen, has forcedthe liquid level in the bottle be-low that in the pan. Now loosenthe tube clamps to bleed theliquid from the gas feed tubes, re-clamp them, and attach one toeach intake pipe.

Attach a length of tubing toeach vent pipe with the other endsof the tubes in a bottle of water(Fig. 1). Open the clamps on thefeed tubes to allow gas to reach the cell andthen lift the vent tubes to the surface of thewater, bleeding the air which has beentrapped in the cell during assembly. As soonas the cell begins to produce current, asshown by the action of a motor or ammeter,replace the tube ends in the water to preventloss of fuel.

Principle of Operation. As the oxygen(O2) enters the cell, it is adsorbed by theelectrode (cathode) on its side (Fig. 6) and,aided by the platinum-black catalyst, is splitinto oxygen atoms (O). These atoms reactwith the water molecules in the electrolyte(KOH + H2O) and p r o d u c e nega t ive lycharged hydroxyl (OH~) ions. In this processthe cathode becomes positively charged by aloss of electrons.

The hydroxyl ions migrate through theelectrolyte and react with hydrogen atoms

(H), which have been formed from hydrogengas (H2) on the opposite electrode (anode),to form water again. The anode receiveselectrons in the process, and when a load cir-cuit is connected between the electrodes, elec-trons will flow to the cathode from the nega-tively charged anode.

A Fuel Cell Test Circuit is set up by wiringan ammeter and a variable resistor parallelto a voltmeter (Fig. 7). The output of thecell can be plotted on a graph to show its per-formance. Various electrolytes (sodium hy-droxide is a good substitute), electrodes andcatalysts (finely divided nickel, platinum, orcarbon) may be tested. Fig. 8 shows the per-formance curve of the cell described here.By observing the elementary rules of elec-tricity, experiments can be conducted withseveral fuel cells wired either in parallel orin series.

Timing Tape Recordings

• If your tape re-corder has no provi-sion for timing reelsof recording tape, youcan do this easily bymeans of a strip ofmasking tape placednear the spindle. Start

a recording running through the machine,and mark the masking tape with a pencil atfive-minute intervals, in alignment with theamount of the tape on the reel. Then removethe strip of tape and type in the numbers ofminutes as shown. Be sure to replace themasking tape in exactly the same position orthe markings may prove inaccurate. Place asimilar marking tape arrangement near theother spindle.—JOHN A. COMSTOCK.

Squeeze Bottle Dusts Capacitor• An empty plastic squeeze bottle makes ahandy air-gun for blowing the plates of avariable capacitor clean.—JOHN A. COMSTOCK.

DECEMBER, 1960 109