Ni-Fe-Mo alloys have been electroplated by using suitable bath solution and plating conditions. SEM and XRD analysis showed that the deposited alloys are partially amorphous. Polarization studies indicated a dependence of the hydrogen evolution mechanism on temperature and current density. The alloys exhibited sufficiently low hydrogen over voltage even on prolonged electrolysis in 30 KOH. Electrokinetic parameters are evaluated for hydrogen evolution reaction on Ni-Fe-Mo alloys. Copyright Â© 1999 John Wiley & Sons, Ltd

Mayanna, S.M

Ramesh, L.

Sheshadri, B.S.

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INTERNATIONAL JOURNAL OF ENERGY RESEARCHInt. J. Energy Res., 23, 919}924 (1999)SHORT COMMUNICATIONELECTROLYTIC PREPARATION AND CHARACTERIZATION OFNi}Fe}Mo ALLOYS: CATHODE MATERIALS FOR ALKALINEWATER ELECTROLYSISL. RAMESHs, B. S. SHESHADRI AND S. M. MAYANNA*Department of Post Graduate Studies in Chemistry, Central College, Bangalore University, Bangalore 560 001, IndiaSUMMARYNi}Fe}Mo alloys have been electroplated by using suitable bath solution and plating conditions. SEM and XRDanalysis showed that the deposited alloys are partially amorphous. Polarization studies indicated a dependence of thehydrogen evolution mechanism on temperature and current density. The alloys exhibited su$ciently low hydrogen overvoltage even on prolonged electrolysis in 30% KOH. Electrokinetic parameters are evaluated for hydrogen evolutionreaction on Ni}Fe}Mo alloys. Copyright ( 1999 John Wiley & Sons, Ltd.KEY WORDS: Ni}Fe}Mo alloys; cathode materials; anomalous codeposition; hydrogen overvoltage; waterelectrolysis; Tafel slope1. INTRODUCTIONAlkaline water electrolysis has become a prominent method of producing hydrogen for H2}O2fuel cells.Extensive work has been done on this process (Bockris and Srinivasan, 1969; Trasatti, 1990; Tilak et al.,1981). Ni}Zn porous electrodes show low hydrogen overvoltage and their catalytic activity depends on themorphology of the surface and the design of catalytic particles (Santos et al., 1992; Wendt, 1994). Catalyticactivity is enhanced by adding oxides of iron and cobalt to the electrolytic cell (Schmidt and Wendt, 1994).Electrolytically prepared Ni}P (P&3%) electrodes are used as a cathode material for alkaline waterelectrolysis (Ivo, 1995). Surface modi"cation by foreign elements have been shown to enhance the catalyticactivity (Yoshida and Morimoto, 1994). Su$ciently low hydrogen overvoltage has been observed onFe}Co}W alloys during alkaline water electrolysis (Ramesh et al., 1998). Despite many developments in fuelcell technology over the past four and a half decades, the basic understanding of the technology is still in itsinfancy. The coated materials lose their catalytic activities during operation because of the surface contami-nation of solution components. Hence, it is aimed to develop ternary alloys of Ni, Fe and Mo byelectroplating techniques with the idea of using them as e!ective cathode materials for production ofhydrogen for H2}O2fuel cells.2. EXPERIMENTALThe deposition of alloys was carried out on copper foils (99)9%). The copper surface was mechanicallypolished by 4/0 emery paper with ethanol as lubricant and electropolished in 60% (v/v) H3PO4at a cell*Correspondence to: S. M. Mayanna, Department of Post Graduate Studies in Chemistry, Central College, Bangalore University,Bangalore 560 001, India. Email: bang@sirnetb.ernet.ins Indal Electronics Limited, 12A Industrial Area, Nanjanagud, Mysore 571 301, India.Contract/grant sponsor: AICTECCC 0363}907X/99/100919}06$17.50 Received 30 October 1998Copyright ( 1999 John Wiley & Sons, Ltd. Accepted 5 November 1998potential of 1.2 V for 30 min with a large copper foil as cathode (Jacquet, 1949). The surface waswashed with 10% H3PO4solution and "nally rinsed with distilled water and used for deposition.Constant temperature and pH were maintained during each experiment. Polarization experimentswere carried out under galvanostatic condition by using a potentiostat/galvanostat (EG & G PAR 273A).A saturated calomel electrode and a platinum #ag were used as reference and counter electrodes,respectively. Deposition potentials were recorded at regular intervals of time using a digital voltmeter with anaccuracy of#2 mV.The deposited samples were stripped in HNO3solution (1 : 3) and the composition of the coatingswas obtained by using atomic absorption spectrophotometer (Varian Spectra AA320). Surface andstructural characteristics of the samples were obtained by using scanning electron microscopic (Jeol JSM)and X-ray di!raction (Philips PW 1142) techniques respectively. Experiments were repeated to ensurereproducibility.3. RESULTS AND DISCUSSIONMany organic compounds were advantageously used as complexing agents in the plating bath solution.Triammonium citrate (TAC) was found to be more suitable to complex metal ions in alkaline condition.Detailed studies were carried out by varying bath composition and plating conditions and a workableprocedure (Table 1) was developed to get good quality deposits with appreciable catalytic activity.3.1. Plating variablesExperiments were carried out to study the e!ect of plating variables, viz., metals ion ratio inthe bath solution, pH, cd, temperature and the concentration of the complexing agents on the composi-tion of the alloy. The pH of the bath solution was maintained as constant (pH 9) by using NaOHand boric acid.Ni}Fe}Mo alloys were electroplated at a current density of 1)5 A dm~2 to a constant thickness (20 lm) at303 K and pH 9 from a bath solution containing various metal ratios in the presence of 0)32 mol l~1 TAC.Under these plating conditions, preferential deposition of nickel over iron was noticed (Figure 1). TAC asa complexing agent reduced the anomalous co-deposition of iron over nickel (Brenner, 1969).Experiments were also carried out at di!erent cds using bath solution containing de"nite metal ion ratioand 0)32 mol l~1 TAC at 303 K and pH 9. The % of nickel in the deposit increased, whereas iron andmolybdenum contents decreased with increase in cd (Figure 1). The alloys were electroplated at varioustemperatures (303}343 K) keeping other variables as constant. There was no signi"cant change in the alloycomposition with increase in temperature. The current e$ciency was found to increase with increase in pHand temperature, but decreased with increase in current density.Table 1. Bath composition and operating conditionsBath composition mol dm~3 Operating conditionsNiSO46H2O 0)28 pH 9)0FAS 0)08 Temperature 303 KTriammonium citrate 0)32 Current density 15 mAcm~2Ammonium chloride 0)30 Agitation 180 rpmBoric acid 0)28 Cathode Copper foilNa2MoO42H2O 0)08 Anode SS 316Time 60 min920 SHORT COMMUNICATIONInt. J. Energy Res., 23, 919}924 (1999)Copyright ( 1999 John Wiley & Sons, Ltd.Figure 1. Dependence of alloy composition on bath composition and current densityFigure 2. SEM photograph of FeNiMo (24 : 64 : 12) alloy obtained at 303 K3.2. Surface and structural analysisNi}Fe}Mo alloys electroplated under various plating conditions were examined under a metallurgicalmicroscope. In a range of temperature, pH and cd studied, the alloy deposits appeared to be amorphousand mat in texture. SEM photograph of the alloy obtained at 303 K for 60 min at 1)5 Adm~2 is shownin Figure 2. The alloy deposits obtained under optimum conditions (Table 1) were subjected to X-raySHORT COMMUNICATION 921Copyright ( 1999 John Wiley & Sons, Ltd. Int. J. Energy Res., 23, 919}924 (1999)di!raction analysis to characterize the phases present. The X-ray data is given in Table 2. These results showthe presence of multiphases in the deposit. However, the peak intensities were slightly broadened indicatingpartial amorphous nature of the deposit.3.3. Catalytic activityThirty percent KOH (wt%) is extensively used in electrolytic cell to produce hydrogen for H2}O2fuel cell(Dobos, 1975). To understand the electrocatalytic activities of the deposited alloys for hydrogen evolutionreaction, detailed galvanostatic polarization experiments were carried out on electroplated alloys havingdi!erent compositions in 30% KOH at di!erent temperatures (303}343 K). Among all the alloys deposited,only Fe}Ni}Mo (24 : 64 : 12) with high nickel content was found to be a better catalyst for the hydrogenevolution reaction. Hence, the alloy with the above composition was used for detailed investigation. Some ofthe results obtained with Ni}Fe}Mo alloys are shown in Figure 3. The Tafel diagram consists of two Tafelregions with di!erent reaction mechanisms for hydrogen evolution reaction in the cd range chosen.Electrochemical parameters were evaluated and summarized in Table 3.Table 2. XRD data of Fe}Ni}Mo codepositsObserved Std ASTM Phased (A) d (A)2)083 2)086 Cu(110)2)002 2)000 Fe(100)1)983 1)980 Ni(111)1)826 1)822 Fe(104)1)639 1)640 Fe(201)1)428 1)428 MoO3(110)1)232 1)232 Fe(103)1)012 1)016 Ni(302)Co Ka radiationFigure 3. Tafel plots obtained on FeNiMo (24 : 64 : 12) alloy deposit in 30% KOH at various temperatures922 SHORT COMMUNICATIONInt. J. Energy Res., 23, 919}924 (1999)Copyright ( 1999 John Wiley & Sons, Ltd.Table 3. Electrochemical parameters for hydrogen evolution reaction on Fe}Ni}Mo (24 : 64 : 12) codeposits atdi!erent temperaturesTemp. b-08b)*’)a-08a)*’)i0 -08i0 )*’)g100(K) (mVdeg~1) (mVdeg~1) (mA cm~2) (mA cm~2) (mV)303 43 163 1)39 0)37 1)0 11)2 148323 43 163 1)49 0)40 1)15 13)4 126343 44 164 1)54 0)43 1)90 15)2 104Figure 4. Arrhenius plots under (a) low (b) high polarization region with FeNiMo (24 : 64 : 12) alloy in 30% KOHThe exchange current density (i0) value for hydrogen evolution with Ni}Fe}Mo alloy was much highercompared to the values obtained on Ni or Ni}Zn or Ni}Fe}Zn (Conway et al., 1987) alloys. The high valuesof i0indicated increased surface activity of the electrodes for hydrogen evolution reaction. The observed twoTafel slopes in the present system did not agree with Ni}Zn or Ni}Co}Zn alloys. However, they agreed verywell with the system developed by Arul Raj and Vasu (1990).Temperature has slight e!ect on Tafel slope (Table 3). This fact contradicts the classical theories on thesubject and is accounted by Conway et al. (1989). However, the transfer coe$cient (a) varied withtemperature. The values of activation energy, (E!) for hydrogen evolution reaction were evaluated from theArrhenius plots (Figure 4) for both low and high Tafel regions.Continuous operation test up to 40 h were conducted using the deposited alloys in 30% KOH at 343 Kat a cd of 10 A dm~2 (Figure 5). The electrode exhibited almost steady overpotential of!104 mV upto 40 hwhich is much lower than the values observed with mild steel (!380 mV) or Ni}Zn or Ni}Co}Zn alloys. Thisindicates the stability of cathode material for prolonged electrolysis for electrolytic production of hydrogen.4. CONCLUSIONTriammonium citrate (TAC) in the plating bath solution has reduced the extent of anomalous codepositionof iron over nickel. Bath composition and plating conditions were optimized to get Ni}Fe}Mo alloys withSHORT COMMUNICATION 923Copyright ( 1999 John Wiley & Sons, Ltd. Int. J. Energy Res., 23, 919}924 (1999)Figure 5. Variation of overpotential on FeNiMo alloy (24 : 64 : 12) with time in 30% KOH at 100 mAcm~2 and 343 Kgood catalytic activity for cathodic evolution of hydrogen from alkaline water electrolysis. The alloys werepartially amorphous and exhibit su$ciently low hydrogen overpotential in alkaline solution. The mechanismof hydrogen evolution reaction depends on the current density range investigated.ACKNOWLEDGEMENTSThe authors thank the AICTE, New Delhi for "nancial support.REFERENCESArul Raj, I. and Vasu, K. I. (1990). J. Appl. Electrochem., 20, 32.Bockris, J.O’M. and Srinivasan, S. (1969). Fuel cells and their Electrochemistry, McGraw-Hill, New York, p. 289.Brenner, A. (1969). Principles of Alloy Deposition, Vol II, Academic Press, New York, p. 347.Conway, B. E., Bai, L. and Sattar, M. A. (1987). Int. J. Hydrogen Energy, 12, 607.Conway, B. E., Tessier, D. F. and Wilkinson, D. P. (1989). J. Electrochem. Soc., 136, 2486.Dobos (1975). Electrochemical Data, Elsevier, New York, p. 85.Ivo, P. (1995). Electrochim. Acta, 40, 1663.Jacquet, P. A. (1949). J. Metal Finishing 47, 48.Ramesh, L., Sheshadri, B. S. and Mayanna, S. M. (1998). „rans IMF 76, 101.Santos, M. B. F., Paseda Silva, E., Andrade Jr. P. and Dias, J. A. F. (1992). Electrochim. Acta, 37, 29.Schmidt, H. and Wendt, H. (1994). Electrochim. Acta, 39, 1763.Tilak, B. V., Lu, P. W. T., Colmen, E. E. and Srinivasan, S. (1981). In Comprehensive „reatise on Electrochemistry, Vol 2, Bockris,J.O’M., Conway, B. E., Yeager, E., and White, R. E., (Eds), Plenum Press, New York, p. 1.Trasatti, S. (1990). In Electrochemical Hydrogen „echnologies, H. Wendt (Ed.), Elsevier, Amsterdam, p. 1.Wendt, H. (1994). Electrochim. Acta, 39, 1749.Yoshida, N. and Morimoto (1994). Electrochim. Acta, 39, 173.924 SHORT COMMUNICATIONInt. J. Energy Res., 23, 919}924 (1999)Copyright ( 1999 John Wiley & Sons, Ltd.

Electrolytic preparation and characterization of Ni-Fe-Mo alloys: Cathode materials for alkaline water electrolysis

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Electrolytic preparation and characterization of Ni-Fe-Mo alloys: Cathode materials for alkaline water electrolysis

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