• Energy Research

Abstract The aim of this work is to determine the optimum operating conditions for the process of preparing anode electrocatalysts for direct sodium borohydride fuel cell (DSBHFC). Pt–Au/C electrocatalysts were studied as the anode catalysts while Pt/C were chosen as a cathode catalyst. Anode electrocatalysts were produced by the precipitation method. In this work, pH, temperature, drying time and Pt/Au ratio were selected as independent process parameters and their effects on dependent parameters, such as power density and hydrogen production rate, were investigated using response surface methodology (RSM). Based on this methodology, it was found that the maximum power density and the minimum hydrogen production rate were 354.4 mW cm−2 and 30 ml min−1 respectively. These findings were obtained at 90 °C, 9.27 pH, 61.07 h of drying time, and 93.54% Au ratio to total metal ratio.

Abstract In this study, optimization of the hot-pressing parameters in manufacturing of the MEA (membrane electrode assembly) is carried out using RSM (response surface method). The important parameters to be optimized in the MEA production are temperature, pressure and the processing (pressing) time. Therefore, the studied temperature, pressure and pressing time intervals are 80–130 °C, 10–100 kg cm−2, and 1–5 min, respectively. In the RSM, the objective function to be maximized is power density, whereas temperature, pressure and pressing time are all independent variables. This method generates a non-linear quadratic equation in terms of independent parameters. Based on contour plots and variance analysis, two optimum operation conditions are determined with respect to maximum power densities. In the first case; where the manufacturing cost and difficulties in operating conditions are taken into account, maximum power density is 862 mW cm−2 at the manufacture parameters of 97 °C, 66 kg cm−2 and 3.6 min. In the second case; where temperature, pressure and hot-pressing time are set to minimum values in order to save energy and manufacturing time, maximum power density of 768 mW cm−2 is achieved at 87 °C, 48 kg cm−2 and 1.15 min.

Abstract Borohydride has been considered as a potential fuel for the fuel cell application due to its high energy density. A DBFC (direct borohydride fuel cell) is an electrochemical device that converts chemical energy stored in borohydride and oxidant directly to electrical energy as long as the fuel and oxidant is supplied. One of the main problems encountered in a DBFC is the simultaneous hydrolysis of BH4− at the anode surface. The hydrolysis decreases the fuel utilization and fuel cell performance, since hydrogen bubbles hinder the contact of catalyst with reactant. This study investigates the effect of operating conditions (cell temperature, borohydride concentration, flow rates of fuel and oxidant) on DBFC performance by RSM (response surface methodology). PtRu/C is used as the anode catalyst to systematically investigate the effect of hydrogen evolution rate on the fuel cell performance. The maximum power density is obtained at 80 °C fuel cell temperature, 0.5 M NaBH4 concentration, 5 cm3 min−1 flow of anolyte and 100 cm3 min−1 flow of oxygen.

Abstract Direct borohydride fuel cells (DBFC) are considered as attractive energy suppliers because of their high electrochemical activity, open circuit potential, energy storage capacity, and power performance at ambient temperature. For the successful commercialization of the DBFCs, cost effective and high performance cells should be produced. In this study, the analysis and optimization of the DBFC operation conditions are carried out with Design Expert software central composite tool. Power density is chosen as a response (dependent) parameter and cell temperature, borohydride concentration, anode and cathode flow rates and catalyst loading are chosen as independent parameters. Based on ANOVA (analysis of variance) analyses, the maximum power density of 108.5 mW cm −2 is obtained at cell temperature of 79.8 °C, borohydride concentration of 1.5 M, anode flow rate of 5 cm 3 min −1 , cathode flow rate of 0.1 dm 3 min −1 and PtRu/C catalyst loading of 0.7 mg cm −2 .

Abstract The water management is critical to achieve the full potential of PEMFC (polymer electrolyte membrane fuel cells). The surface contact angle and roughness properties of bipolar plate are the main factors affecting water management in a fuel cell and PEMFC performance. The effects of the contact angle and roughness of polymer composite bipolar plate and hydrogen flow rate on power density of PEMFC are analyzed by RSM (response surface methodology) in this study. Fuel cell performance tests are carried out at different hydrogen flow rates by using composite bipolar plates having different values of contact angle and roughness. We observed that the power density of the fuel cell increases with the increase in the hydrogen flow rate due to the increase in hydrogen transport on the anode surface both with respect to contact angle and roughness. At the constant hydrogen flow rate, the power density shows a maximum with the increase in both contact angle and Ra (surface roughness). The optimum values of the contact angle and hydrogen flow rate for the studied range are 81.2° and 1.87 dm 3 min −1 , respectively. In addition, the maximum fuel cell performance is obtained at roughness of 1.69 μm and hydrogen flow rate of 1.97 dm 3 min −1 .

In this study, the production of bio-oil from the pyrolysis of furniture sawdust, waste lubricating oil and their mixtures were investigated under certain operating conditions in the presence of lime and zeolites, by using a laboratory scale horizontal tubular reactor placed in a furnace. The main focus was to investigate the mutual effect of lime and commercial zeolite on the amount of the bio-oil production from furniture sawdust and waste lubricating oil. The selected operating parameters were pyrolysis temperatures and heating rate of 300°C and 650°C and flash heating or gradual heating rate (30°C/min). Additionally, three different additives were tested as catalysts; namely, lime (CaO), commercial zeolite (4A) and a natural zeolite (klinoptilolite). The amount of the produced bio-oil was analyzed by gas chromatography–flame ionization detector. The distribution of solid, liquid and gaseous products was determined for each operational condition. It was seen that the amount of the bio-oil was influenced by the amounts of sawdust and zeolite in the mixture. Experimental results showed that higher temperatures were more effective for the higher bio-oil amount. Additionally, heating rate was quite significant at 300°C whereas it has a minor effect on the bio-oil amount at 650°C. The highest bio-oil yield was obtained for the mixture of sawdust and waste lubricating oil in the presence of both lime and commercial zeolite with flash heating rate at 650°C.