Heat induced voltage generation in electrochemical cell containing zinc oxide nanoparticles Anindita Mondal a, * , Ruma Basu b , Sukhen Das a , Papiya Nandy a a Physics Department, Jadavpur University, Raja S. C. Mallick Road, Kolkata 700032, India b Physics Department, Jogamaya Devi College, Kolkata 700026, India article info Article history: Received 6 October 2009 Received in revised form 27 January 2010 Accepted 28 January 2010 Available online 5 March 2010 Keywords: Thermo-voltage Zinc oxide nanoparticle Electrochemical cell Planar lipid membrane Energy conversion efﬁciency abstract The quest for alternative energy sources has stimulated interest in several new materials. Using an aqueous suspension of zinc oxide nanoparticles in specially-designed electrochemical cells we have observed signiﬁcant voltage (maximum 498.0 mV) and storage capacity (~60 h) upon thermal excitation. Voltage increased gradually with increasing temperature. The cells exhibited reasonable energy conversion efﬁciency (maximum 1.05%). Moreover, increases in efﬁciency and storage duration were observed with the insertion of a planar lipid membrane (PLM) within the electrochemical cell, since the hydrophobic barrier of the lipid membrane hindered back recombination of the charges produced by thermal excitation. The novelty of the cells lies in the fact that voltage was generated by utilizing the heat energy of solar radiation, as opposed to the light quanta of the solar inﬂux used in conventional photovoltaic cells. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The stable colloidal suspension of quantum dots of metal–oxide semiconductors has received much attention due to its application in photonics [1], photocatalytic reduction [2], the eradication of environmental pollutants [3], etc. Zinc oxide (ZnO), a metal–oxide semiconductor with the wide band gap of 3.3 eV, exhibits some special properties in its nano form, such as larger speciﬁc surface, sensitivity to surrounding perturbants, high surface activity, piezoelectric properties, etc. [4]. Because of these special proper- ties, it has received widespread attention in recent years [5]. Owing to the wide band gap, ZnO nanoparticles (ZnO NPs) have numerous applications in various different ﬁelds such as solar cells [6–8], transistors and optical switches [9], etc. At present, harnessing solar energy using inexpensive tech- niques is an important challenge, and several new concepts and techniques have been developed for solar-to-electrical energy conversion [10–12], replacing traditional photovoltaic devices based upon p–n junction diodes [13–16]. ZnO NPs are being used in solar energy conversion systems, owing to their stability against photo corrosion and suitable photochemical properties. In fact, its photochemical properties are quite similar to those of TiO 2 , which is widely used in photovoltaic cells [17]. Solar energy conversion efﬁciencies of 0.4% for 10 nm ZnO crystalline ﬁlms [18] and 2% for Ru(II) complex-sensitized photo-electrochemical solar cells based on nanostructured ZnO electrodes [19] have already been reported. Suliman et al. demonstrated efﬁciency as high as 1.55% for photo- electrochemical solar cell based on ZnO nanosheets [20]. In our laboratory we have observed voltage generation in elec- trochemical cells using different photosensitive dyes upon illumi- nation and thermal excitation [21–23]. The special properties of ZnO NPs have led us to explore the possibility of their use in solar energy conversion. For this purpose we have devised an electro- chemical cell consisting of two compartments, one of which is ﬁlled with an aqueous suspension of ZnO NPs, while the other is ﬁlled with hydrochloric acid (HCl) solution. The two compartments are separated by either a platinum foil or a planar lipid membrane (PLM). Keeping the cells at different constant temperatures we observed, for the ﬁrst time, thermo-voltage generation (TVG) with high magnitude and energy conversion efﬁciency (h). The value of h increased with increasing cell temperature within our experi- mental range (30–50  C). Since the temperature required for TVG is not very high, the thermal excitation caused by solar radiation alone is enough to produce signiﬁcant voltage. 2. Materials and methods For sample preparation we have used zinc acetate dihydrate [Zn(OAc) 2 $2H 2 O] from Merck, India, and lithium hydroxide * Corresponding author. Tel.: þ91 33 9432373165. E-mail address: sunimondal@yahoo.com (A. Mondal). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2010.01.035 Energy 35 (2010) 2160–2163