The objective of the current work is to support the design of a pilot hydrogen and electricity producing plant that uses natural gas (or biomethane) as raw material, as a transition option towards a 100% renewable transportation system. The plant, with a solid oxide fuel cell (SOFC) as principal technology, is intended to be the main unit of an electric vehicle station. The refueling station has to work at different operation periods characterized by the hydrogen demand and the electricity needed for supply and self-consumption. The same set of heat exchangers has to satisfy the heating and cooling needs of the different operation periods. In order to optimize the operating variables of the pilot plant and to provide the best heat exchanger network, the applied methodology follows a systematic procedure for multi-objective, i.e. maximum plant efficiency and minimum number of heat exchanger matches, and multi-period optimization. The solving strategy combines process flow modeling in steady state, superstructure-based mathematical programming and the use of an evolutionary-based algorithm for optimization. The results show that the plant can reach a daily weighted efficiency exceeding 60%, up to 80% when considering heat utilization.

Microbial fuel cells (MFCs) are energy transducers, which through the metabolic reactions of facultative anaerobic microorganisms, transform the energy in organic matter directly into electricity. Extrinsic parameters such as hydraulic retention time, fuel quality (type and concentration) and physicochemical environment of electrodes and biofilms (e.g., temperature, pH, salinity, and redox), can all influence system efficiency. This work proposes that MFCs can be "fine-tuned" by adjustment of any of the physicochemical conditions including redox potential; in this context, an entirely novel method was investigated as a practical means of tuning, modulating and monitoring the redox potential within the electrode chambers. The method uses additional electrodes - known as 3 and 4-pins for anode and cathode chambers, respectively - which can be used in individual units, modules, cascades or stacks, for optimising the production of a large variety of chemicals, as well as biomass, water and power. The results have shown that the power output modulation resulted in an up to 79% and 33% increase, when connected 3 and 4 pins, respectively. Apart from power improvement, this study also demonstrated a method of open circuit potential (OCP) sensing, by using the same additional electrodes to both monitor and control the MFC signal in real time.

Fuel flexibility is a significant advantage of solid oxide fuel cells (SOFCs) and can be attributed to their high operating temperature. Here we consider a direct internal reforming solid oxide fuel cell setup in which a separate fuel reformer is not required. We construct a multidimensional, detailed model of a planar solid oxide fuel cell, where mass transport in the fuel channel is modeled using the Stefan-Maxwell model, whereas the mass transport within the porous electrodes is simulated using the Dusty-Gas model. The resulting highly nonlinear model is built into COMSOL Multiphysics, a commercial computational fluid dynamics software, and is validated against experimental data from the literature. A number of parametric studies is performed to obtain insights on the direct internal reforming solid oxide fuel cell system behavior and efficiency, to aid the design procedure. It is shown that internal reforming results in temperature drop close to the inlet and that the direct internal reforming solid oxide fuel cell performance can be enhanced by increasing the operating temperature. It is also observed that decreases in the inlet temperature result in smoother temperature profiles and in the formation of reduced thermal gradients. Furthermore, the direct internal reforming solid oxide fuel cell performance was found to be affected by the thickness of the electrochemically-active anode catalyst layer, although not always substantially, due to the counter-balancing behavior of the activation and ohmic overpotentials.