: A : O 646 CO 2. ( Rh 2 O 3,Nb 2 O 5,Cr 2 O 3,V 2 O 5,WO 3 ) Pt/ H x MoO 3. Vol. 8 No. 4 Nov EL ECTROCHEMISTR Y : (2002)

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1 EL ECTROCHEMISTR Y Vol 8 No 4 Nov 2002 : (2002) ,,, (, ) 3 :,, ;,, 2 : ; ; ; ; : O 646 : A,,, [1 ],, [2, ] ; [3 ] ; [4 ], ;, CO 2, [5 ] [6 11, ] ( Rh 2 O 3,Nb 2 O 5,Cr 2 O 3,V 2 O 5,WO 3 ) [12 ], WO 3 MoO 3 [13, ] [14 ] [15 ], GC / [16 ] [17 Pt/ H x MoO 3 ], : , : , Tel : (86-20) ,E- mail edu cn : (970319),, ( )

2 4 : MODEL 553 MODEL567 ( ECO INSTRUMEN TS) X Y ( T YPE 3036, HO KUSHIN EL ECTRON IC CO) EG &G273 (, M270 ), cm 2, ; Ag/ AgCl, H 2 SO 4 Na 2 MoO 4, 200 mv/ s ml/ L H 2 SO 4, a 1 a, b 1 b, [ 18 ] [18 ] mol/ L Na 2 MoO mol/ L H 2 SO 4 1, 0 3 V,,, V c 1, 1 0 V ( ) mol/ L H 2 SO 4 ( ) 0 05 mol/ L Na 2 MoO 4 + 2, 2 5 mol/ L, 0 5 mol/ L H 2 SO 4 ( ), 1 ( ) 0 3 V, 2 ( ) Fig 1 Cyclic voltammograms of platinum,, 0 75 V electrode in 0 5 mol/ L H 2 SO 4 ( ) 3 H 2 SO 4 ( dash line ) and 0 05 mol/ L 5 4 mol/ L 2 3, Na 2 MoO mol/ L H 2 SO 4, (solid line) solutions,scan rate :200 mv/ s

3 mol/ L H 2 SO mol/ L Na 2 MoO 4 Na 2 MoO 4 Fig 2 Cyclic voltammograms of polycrystalline plat2 inum electrode in 2 5 mol/ L H 2 SO mol/ L Na 2 MoO 4 solution at different scan rates : mv/ s mol/ L H 2 SO mol/ L Fig 3 Cyclic voltammograms of polycrystalline plat2 inum electrode in 5 4 mol/ L H 2 SO mol/ L Na 2 MoO 4 solution at different scan rates : mv/ s mol/ L Na 2 MoO 4 0 V, 3 7mol/ L,, 4 5 mol/ L, : MoO 2 4 -, p H [19, 20 ],, MoO 2 4 -, ( ) 4 Na 2 MoO 4, Fig 4 Relationship between reduction current of 0 05 MoO mol/ L Na 2 MoO 4 and H 2 SO 4 concentration H x MoO 3, :

4 4 : 423 MoO (2 + x) H + + x e = H x MoO 3 + H 2 O (0 < x 2) ( ) ( ), H x MoO 3, x ;, x ; H 2 MoO 3,, MoO MoO 3 H 2 O,, : mol/ L H 2 SO mol/ L 2 5 mol/ L H 2 SO mol/ L Na 2 MoO 4 (1) 5 4 mol/ L H 2 SO mol/ L Na 2 MoO 4 ( 1) 5 4 mol/ L H 2 SO mol/ L Na 2 MoO 4 ( 2) + Na 2 MoO 4 (2) 0 3 V, a) 0 min, b) 2 min,c) 30 min + 0 9V, Fig 5 Redox coubomb quantity of polycrystalline plat2 5,10 s inum electrode in 2 5 mol/ L H 2 SO V Na 2 MoO 4, a,b,c a 1,b 1,c 1 mol/ L Na 2 MoO 4 (1) and 5 4 mol/ L H 2 SO mol/ L Na 2 MoO 4 (2) solutions pause time at OCP a) 0 min, b) 2 min c) 30 min 0 min 2 min 30 min, 0 9 V,,,, 2 3, ( H x MoO 3 ) ads H x- y MoO 3 + y e + yh + (0 < x < 1,0 < y < x) [21 ],, 0 5 mol/ L H 2 SO mol/ L Na 2 MoO 4, 0 3 V 10 s, 0 5 mol/ L Na 2 SO mol/ L HCOOH, 6 a 6 a 0 a 0 5 mol/ L Na 2 SO mol/ L H 2 SO 4

5 a a,, (0 071 ma), (0 038 ma) 2, CO ;, (CO) ads : ( CO) ads + 4 ( H x MoO 3 ) ads + H 2 O 6 CO ( H x MoO 3 ) ads, 200 mv/ s ( H x MoO 3 ) ads Ω ( H x MoO 3 ) ads + a 0 ) 0 5 mol/ L Na 2 SO 4 CV 0 5H e ;a) 0 5 mol/ L, H 2 SO 4 10 s ; a ), 10-4 mol/ L Na 2 MoO mol/ L H 2 SO 4 10 s Fig 6 Electrocatalysis of fomic acid on platinum elec2 3 trode modified with or without hydrogen molyb2 denum bronzes (1) a 0 ) Cyclic voltammogram of platinum electrode in 0 5 mol/ L Na 2 SO 4 solution ;a) The platinum, 0 05 mol/ L electrode was pre- reduced for 10s in 0 5 mol/ L 2 5 mol/ L H 2 SO 4, H 2 SO 4 solution without molybdate ; a ) The ; H 2 SO 4 platinum electrode was pre- reduced for 10s in mol/ L, 3 5 mol/ L H 2 SO 4 solution with 10-4 mol/ L (2) Na 2 MoO 4,,

6 4 : 425 Electrocatalytic Oxidation of Formic Acid on Molybdate- Modified Platinum Electrode DU J un- hua,xu Xue- hui,l I Hong,CHEN G Hong-yu,L I Wei- shan 3 ( Depart ment of Chemist ry, South China Norm al U niversity, Guangz hou , China) Abstract : The electrochemical behavior of molybdates on a platinum electrode in H 2 SO 4 solu2 tions with different H 2 SO 4 concentrations was studied by cyclic voltammetry and double chronoamperomet ry Molybdates were reduced to adsorb hydrogen molybdenum bronzes on t he platinum electrode in H 2 SO 4 solutions during cathodically potential sweep The hydrogen molyb2 denum bronzes were oxidized to different forms of hydrogen molybdenum bronzes wit h less hydro2 gen, depending on the H 2 SO 4 concentration Platinum electrode was modified by these hydrogen molybdenum bronzes However, this modified electrode was not stable in H 2 SO 4 solutions The modified electrode was used to study the oxidation of formic acid in Na 2 SO 4 solutions It was shown that there was a strong catalysis on the oxidation of formic acid on the modified electrode The peak current of formic acid on the modified electrode was about two times that on unmodified electrode It was also found that the catalysis was weakened when the platinum elecdtrode was under-or over- modified Key words : Platinum, Hydrogen molybdenum bronze, Modification, Fomic acid, Catalyti2 coxidation Reference s : [1 ] Lamy C Electrocatalytic oxidation of organic compounds on noble metals in aqueous solution[j ] Electrochim2 ica Acta,1984,29(11) : [2 ] Watanabe M,Uchida M,Motoo S Application of the gas diffusion electrode to a bachward feed and exhaust (bfe) type methanol anode[j ] J Electroananl Chem, 1986,199 : [3 ] Appleby A J The energy crisis : The electrochemical viewpoint J Electroanal Chem,1981,118 :31 50 [4 ] Srinivasa S Fuel cell for electric utility and transportation application[j ] J Electroanal Chem,1981,118 : [5 ] Watanabe M, Furuuchi Y, Motoo S Electrocatalysis by ad-atoms Part XIII Preparation of ad-electrodes with tin ad- atoms for methanol,formaldehyde and formic acid fuel cells[j ] J Electroanal Chem,1985,191 : 367 [6 ] Parsons R, T Vander Noot The oxidation of small organic molecules :A survey of recent fuel cell related re2 search[j ] J Electroanal Chem,1988,257 :9 45 [7 ] Hogarth M P, Hards G A Direct methanol fuel cells[j ] Platinum Metals Rev,1996,40(4) :

7 [8 ] Yang H,Lu T H,Xue K H,et al Electrocatalytic oxidation of methanol on polypyrrole film modified with platinum microparticals[j ] J Electrochem Soc,1997,144(7) : [ 9 ] Mcnicol B D, Rand D A J, Williams K R Direct methanol-air fuel cells for road transportation[j ] J Power Source,1999,83 :15 31 [10 ] Baldauf M, Preidel W Status of the development of a direct methanol fuel cell[j ] J Power Source,1999, 84 : [11 ] Sattler G Fuel cells going on- board[j ] J Power Source,2000,86 :61 67 [12 ] Collins G C S, Schiffrin D J The electrochromic properties of lutetium and other phthalocyanines[j ] J Electroanal Chem, 1982,139 : [13 ] Li C P, Hercules D M A surface spectrocopic study of sulfided molybdena-alumina catalysis[j ] J Phys Chem,1984,88 : [14 ] Kumagai N, Kumagai N, Tanno K Electrochemical characteristics and structural changes of molybdenum tri2 oxide hydrates as cathode materials for Lithium batteries [J ] J Appl Electrochem,1988,18 (6) : [15 ] Zhang H Q, Wang Y, Fachin E R, et al Electrochemically codeposited platinum/ molybdenum oxide elec2 trode for catalytic oxidation of methanol in acid solution[j ] Electrochemical and Solid- State Letters, 1999, 2 (9) : [16 ] TIAN Li-peng,L I Wei- shan Electrocheical behavior of molybdate and its catalysis on the methanol oxida2 tion[j ] J Power Sources (in Chinese), 2001,25 (2) :72 74 [ 17 ] TIAN Li-peng, L I Wei- shan, L I Hong Catalytic oxidation of methanol on Pt/ H x MoO 4 electrode[j ] Fine Chemicals(in Chinese), 2000,17 : [18 ] Bard A J, Faulkner L R Electrochemical Methods[ M ] New York : John Wiley & Sons, [19 ] Bard A J, Parsona R, Jordan J Standard Potentials in Aqueous Solution[ M ] New York : [20 ] CAO Xi-zhang,ZHAN G Wan- hui,du Rao-guo, et al Inorganim Chemistry Shanghai : Education Press, [21 ] Li W S, Tian L P,Huang Q M,et al Catalytic oxidation of methanol onmolybdate- modified platinum elec2 trode in sulfuric acid solution[j ] J Power Source(in Chinese), 2002,104 :