Metal oxide-​hydroxides of the general formula MO(OH) (M = Ni3+, Co3+ and Mn3+) are actually bronzes of the corresponding quadrivalent metal oxides and should be represented as HxMO2 (x = 1)​.  IR spectroscopic studies show that these compds. do not exhibit any OH stretch.  The protons seem to be delocalized between slabs of MO2

Ganguly, S.

Vishnu, K. P.

ePrints@Bangalore University

Volume IO, number 11,12 MATERIALS LETTERS March 1991 Infrared spectroscopic studies of the oxide-hydroxides of Ni, Co and Mn P. Vishnu Kamath Department sf Chemistry, Central College, Bangalore University, Bangalore 560 001, India and S. Ganguly I.D.L. Nitro Nobel Basic Research Institute, P.O. Box 397, Malleswaram, Bangalore 560 003, India Received 29 August 1990; in final form 25 November 1990 Metal oxide-hydroxides of the general formula MO(OH) (M=Ni’+, Co3+ and Mn’+ ) are actually bronzes of the correspond- ing quadrivalent metal oxides and should be represented as H,M02 (x= 1). Infrared spectroscopic studies show that these com- pounds do not exhibit any hydroxyl stretch. The protons seem to be delocalized between slabs of MOz. Metal oxide-hydroxides of Ni3+, Co3+ and Mn3+ are known to play a major role in the charge-dis- charge cycle of nickel hydroxide [ 11, cobalt hydrox- ide [ 2,3 ] and manganese dioxide [ 41 electrodes re- spectively. A complete characterization of these phases is therefore essential to our understanding of the electrode reactions taking place at these oxide electrodes. In particular the nature of the hydroxyl species in the oxide-hydroxides has not been clearly understood. Melendres et al. [ 5 1, from a study of the Raman spectra of the higher oxides of nickel, have opined that the formulation of the oxide-hydroxide of nickel as NiO(OH) is incorrect. In this commu- nication we report our infrared spectroscopic studies of the oxide-hydroxides of Ni3+, Co3+ and Mn3+ and compare the results with those of the corre- sponding divalent hydroxides. All compounds studied here were prepared by the method of Brauer [6] and characterized by X-ray diffraction. The X-ray diffractograms were found to match with those reported for these compounds in the JCPDS powder diffraction file [ 71. As observed by other authors [ 5,8], the diffraction patterns of the nickel compounds were broad, indicative of poorly ordered samples. All infrared spectra were recorded on a Perkin- Elmer model 684 IR spectrometer with KBr pellets on CsI windows at a resolution of 3 cm- ‘. In fig. 1 are shown the infrared spectra of Ni (OH ) 2 and NiO( OH). The OH stretching region and the metal oxygen stretching region ( 800-200 cm- ’ ) are both shown in detail. Ni(OH), shows a sharp peak at 3630 cm-’ fol- lowed by a broad band from 3500 to 3200 cm-’ in- dicating the presence of both free and hydrogen- bonded hydroxyl groups. Both the a and p forms of Ni(OH)* have varying amounts of water of hydra- tion [ 8,9] and the broad band in the OH stretching region has a significant contribution from the water of hydration. NiO( OH), on the other hand, shows only a broad weak absorption in the range 3600-3 100 cm- ’ precluding the presence of free hydroxyl groups in this compound. In the low-frequency (800-200 cm- ’ ) region, Ni( OH), shows a complex spectrum with broad bands at 525 and 450 cm-’ and a sharp peak at 350 cm-‘. NiO(OH) shows a broad band at 570 cm-’ and a shoulder at 460 cm-‘. In fig. 2 are shown similar results for the cobalt system. Co(OH), shows a sharp OH stretch at 3620 0167-577x/91/$ 03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland) 537 Volume 10, number 11,12 MATERIALS LETTERS WAVENUMBER (cm-‘) 4000 3500 3000 2500 ,, 000 600 400 2c March 1991 Fig. I. Infrared spectra of Ni(OH)I (A) and NiO(OH) (B). cm-’ followed by a broad band in the 3500-3000 cm-’ region. In the low-frequency region it shows a spectrum similar to that of Ni( OH)z with bands at 480 and 440 cm-’ and a sharp peak at 300 cm-‘. CoO(OH), on the other hand, shows a weak broad absorption band in the 3600-3 100 cm-’ region and there is clearly no indication of the existence of any free hydroxyl group. In the low-frequency region, the spectrum of Co0 (OH) is very simple with a single band at 580 cm-‘. There is a pronounced asym- metry on the low-frequency flank. In fig. 3 is shown the spectrum of MnO (OH ) . Once again the 3600-3000 cm-’ region shows no free OH stretching frequency, while the low-frequency region is very complex with bands at 6 10,490,400 and 330 cm-‘, respectively. Structurally well-defined hydroxides of brucite structure exhibit a sharp peak in the OH stretching frequency region [ 5 1, indicating the presence of free hydroxyl groups. The trivalent oxide-hydroxides, which are known to form by the oxidation of the di- valent hydroxides at the oxide electrodes do not show any well-defined OH stretching modes. Free hy- droxyl groups are therefore absent in the oxide-hy- droxides. It may therefore be more appropriate to formulate these compounds as oxides rather than ox- ide-hydroxides. However, the X-ray diffraction pat- terns as well as the infrared spectra of these trivalent phases are different from those of the well-known di- valent oxides of Ni, Co and Mn, indicating that they are not the same. Melendres et al. [ 5 1, from a group theoretical analysis of their Raman spectra, have in- terpreted the trivalent nickel oxide-hydroxide phase as derived from the quadrivalent NiOz. A similar WAVENUMBER (cm11 4000 3500 3000 2500 000 600 400 I I I ” I I I 538 Fig. 2. Infrared spectra ofCo(OH)Z (A) and CoO(OH) (B). Volume 10, number 11,12 MATERIALS LETTERS March 1991 WAVENUMBER (cm-‘) 4000 3500 3000 2503 BOO 600 400 200 Fig. 3. Infrared spectrum of MnO (OH ) conclusion can be extended to the case of Co and Mn as well. The oxide-hydroxides can then be formu- lated as bronzes of the type H,M02 (x= 1). x= 2 represents end members of the series which are well- defined hydroxides of the brucite structure. Brucite structure consists of layers of MO* with the protons sticking out into the interleaving space [ lo]. The OH bond axis is parallel to the c axis of the crystal. The proton layer is saturated as all the oxygens are bound to a proton each. Oxidation appears to occur by proton extraction and when this happens vacancies are created in the proton layers, as some oxygens are no longer bound to a proton. The protons either become delocalized or get positioned at sites which are less well defined than earlier leading to the disappearance of the free hydroxyl stretching mode in these compounds and the phase acquires a bronze-like character. Fig. 4 il- lustrates this model pictorially. This model qualita- tively explains the two observed phenomena: ( 1) Corrigan and Knight [ 111 have evaluated the charge on Ni on an oxidized nickel hydroxide electrode to M b-d2 “MO(OH)” HMOa Fig. 4. Schematic model to explain the bronze-like behaviour of the oxide-hydroxides. The hatched region represents slabs of MO*, 0 represents a proton, 0 represents a vacancy. be 3.6 -t 0.1, a result compatible with the identifi- cation of the phase as HXNi02 (x=0.4). Buss et al. [ 12 ] in similar work on cobalt hydroxide electrodes have achieved an oxidation state of 3.7. (2) The de- localization of the protons also explains the high pro- ton diffusion coefficients [ 13 ] of the nickel hydrox- ide electrodes. Further investigations on the oxide-hydroxides of other metals are currently in progress. References [ 1 ] P. Oliva, J. Leomarde, J.F. Laurent, C. Delmas, J.J. Braconnie, M. Figlarz, F. Fievert and A. de Guibert, J. Power Sources 8 (1982) 229. [2] R.D. Armstrong and E.A. Charles, J. Power Sources 25 (1989) 89. [3] J. Batter, D.H. Buss, H.J. Harms and 0. Glemser, J. Electrochem. Sot. 137 (1990) 173. [4] B.D. Desai, J.B. Femandes and V.N. Kamat Dalal, J. Power Sources 16 (1985) 1. [ 51 C.A. Melendres, W. Paden, B. Tani and W. Walczak, J. Electrochem. Sot. 134 (1987) 762. [ 61 G. Brauer, Handbook of preparative inorganic chemistry (Academic Press, New York, 1965 ) . [ 71 J.V. Smith, ed., Powder diffraction tile, Joint Committee on Powder Diffraction Standards, Pennsylvania ( 1967). [S] B. Mani and J.P. de Neufville, J. Electrochem. Sot. 135 (1988) 800. [9] H. Bode, K. Dehmelt and J. Witte, Electrochim. Acta 11 (1966) 1079. [lo] H. Krebs, Fundamentals of inorganic crystal chemistry (McGraw-Hill, New York, 1968). [ 1 I ] D.A. Corrigan and S.L. Knight, J. Electrochem. Sot. 136 (1989) 613. [ 12 ] D.H. Buss, J. Bauer, W. Diembeck and 0. Glemser, J. Chem. Sot. Chem. Commun. (1985) 81. [ 13) D.M. MacArthur, J. Electrochem. Sot. 117 ( 1970) 729. 539 

Infrared spectroscopic studies of the oxide-​hydroxides of nickel, cobalt, and manganese

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Infrared spectroscopic studies of the oxide-hydroxides of nickel, cobalt, and manganese

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Infrared spectroscopic studies of the oxide-​hydroxides of nickel, cobalt, and manganese

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Infrared spectroscopic studies of the oxide-hydroxides of nickel, cobalt, and manganese