Mechanism of enhanced performance on a hybrid direct carbon fuel cell using sawdust biofuels

Abstract

Biomass is expected to play a significant role in power generation in the near future. With the uprising of carbon fuel cells, hybrid direct carbon fuel cells (HDCFCs) show its intrinsic and incomparable advantages in the generation of clean energy with higher efficiency. In this study, two types of biomass treated by physical sieve and pyrolysis from raw sawdust are investigated on an anode-supported HDCFC. The structure and thermal analysis indicate that raw sawdust has well-formed cellulose I phase with very low ash. Electrochemical performance behaviors for sieved and pyrolyzed sawdust combined with various weight ratios of carbonate are compared in N2 and CO2 purge gas. The results show that the power output of sieved sawdust with 789 mWcm-2 is superior to that of pyrolyzed sawdust in CO2 flowing, as well as in N2 flowing. The anode reaction mechanism for the discrepancy of two fuels is explained and the emphasis is also placed on the modified oxygen-reduction cycle mechanism of catalytic effects of Li2CO3 and K2CO3 salts in promoting cell performance.

Lignocellulose, Cellulose and Lignin as Renewable Alternative Fuels for Direct Biomass Fuel Cells

“…Hybrid direct carbon fuel cells (HDCFC) merge SOFCs and MCFCs, by extending active reaction sites and limiting cathode corrosion. The feasibility for energy generation by using HDCFCs fueled with biomass was investigated in some works [139–141] . First, Lima et al [139] .…”

“…All these results indicate a different dependence of the performance of the cells fueled with raw and pyrolyzed biomass on operating temperature: for pyrolyzed biomass‐fueled DCFCs the increase of cell performance with increasing temperature is clearly due the improvement of the electrochemical reactions with increasing temperature, while for raw‐biomass‐fueled DBFCs, in addition to the electrochemical effects, the improvement of cell performance with increasing cell operation temperature is in particular due to the increase of the in situ biomass pyrolysis degree with increasing the heating segment of the cell, in which the biomass is pyrolyzed. From the direct comparison of the same biomass (wood sawdust [130,140] and rice straw [130] ), before and after pyrolysis, a counteracting effect of the use of raw and pyrolyzed biomass on cell performance was observed, depending on DCFC operating temperature. Indeed, at 750 °C, the DCFC fed with raw biomass showed a higher performance than that fueled with pyrolyzed biomass, [130,140] while at 850 °C an opposite result was observed [130] .…”

“…The feasibility for energy generation by using HDCFCs fueled with biomass was investigated in some works. [139][140][141] First, Lima et al [139] utilized two types of lignin, lignosulfonate (LS) and Kraft (KL) lignin, as fuels in an HDBFC. LiÀ CuÀ NiÀ ZnO composite oxide was used as the cathode, samarium doped ceria (SDC)-(Li/Na) 2 CO 3 composite electrolyte was used as the electrolyte, and a lignin/electrolyte mixture was used the anode.…”

“…As for the other types of high temperature DBFCs all the types of the fuels (H 2 , CO and C) generated from in situ lignin pyrolysis were involved in the power production. Then, Li et al [140] compared the performance of raw and pyrolyzed wood sawdust as fuel in HDCFCs. Structural and thermal analyses showed that raw sawdust presents a well-formed cellulose I phase and a low ash content.…”

“…The effect of operating temperature on the performance of DCFCs fueled with raw and pyrolyzed biomass is shown in Figure 7a, where the MPD at T to MPD at 800°C ratio is plotted vs. operating temperature for both raw biomass-and biocharfed DCFCs using data from different DCFC types and different biomass fuels: [126][127][128][129][130]138] While the MPD T /MPD 800 ratio of biocharfueled DCFCs presents an almost linear increase of with increasing temperature, the MPD T /MPD 800 ratio of raw biomassfueled DCFCs shows a logarithmic growth, with a slow initial growth, following a fast increase. The dependence of the MPD of biomass-fueled DCFCs to the MPD of biochar-fueled DCFCs ratio on operation temperature from literature data, [126,130,131,138,140,141] is shown Figure 7b: the MPD biomass / MPD biochar ratio, with few exceptions, is < 1, meaning that the MPD of cell fed with biochar is higher than that supplied with raw biomass. It has to be observed, however, that this ratio generally increase with operating temperature, in agreement with the data reported in Figure 7a.…”