1. Laboratory of Nanomaterial for Sensors and Energy Faculty of Science University of Yaounde 1 P. O. Box 812 Yaounde Cameroon
2. Laboratoire d'Electrochimie et de Génie des Matériaux Faculté des Sciences Université de Yaoundé Ab B.P. 812 Yaoundé Cameroun
3. Otto-von-guericke-University Magdeburg Chemical Institute Industrial Chemistry Universitâtsplatz 2 39106 Magdeburg Germany
4. Department of Chemistry High Teacher Training College University of Yaounde 1 P. O. Box 49 Yaounde Cameroon
5. Department of Chemistry University of Pretoria Private Bag, X20 Pretoria, Hatfield 0028 South Africa