Thermocells in box and flat cell configurations were demonstrated via simplified design and cost effective materials like activated charcoal and potassium ferri/ferrocyanide solution and MWCNTs respectively. Employing saturated concentrations of potassium ferri/ferrocyanide in aqueous solution as electrolyte in combination with the electrodes resulted in a highly feasible redox-mediated electron transfer. Effects of concentration of potassium ferri/ferrocyanide (0.1 mM, 1 M and 4 M in aqueous medium) on the performance of the devices were analyzed. The electrolyte trapped in agar-agar gel functions as a solid like medium. In the case of box configuration the maximum power density attained being 22.463 W/m2 yielding 20-30% of Carnot efficiency and 0.563 W/m2 for MWCNT based flat cells reaching 0.5-18% higher than the Carnot efficiency. The efficiency of the thermocells at different ΔT from 30 C to 130 C was reported. The power density increased by 14.92 times for activated charcoal thermocell operating in 1 M K 3[Fe(CN)6]/K4[Fe(CN)6] at ΔT = 60 C in comparison with MWCNT based thermocells at the same ΔT. Other low cost electrode materials like activated charcoal, acetylene black were employed to study the performance of thermocells. Cells were connected in series and parallel to study the feasibility of performance improvement at different ΔT. © 2013 Brazilian Metallurgical, Materials and Mining Association.