Experimental investigation and analyses of continuous type hybrid photoelectrochemical hydrogen production systems
Hydrogen is a highly versatile energy carrier that may become one of the key pillars to support the future CO2-free energy infrastructure. When used in fuel cells, H2 is converted to water and it gives little or zero exhaust of greenhouse gases. For H2 economy to succeed, it needs to be produced in a clean, sustainable, reliable, and feasible way. The main objective of this study is to develop and investigate a continuous type hybrid photoelectrochemical-chloralkali H2 production reactor that converts the by– products into useful industrial commodities (i.e., Cl2 and NaOH). This system maximizes solar spectrum use by taking advantage of photocatalysis and PV/T. Furthermore, by using electrodes as electron donors to drive the photochemical reaction, the potential of pollutant emissions are minimized. Four different processes are tested by using the present reactor: electrolysis, PEC, chloralkali, and PEC-chloralkali. During all processes, the present reactor is tested under four temperatures (20, 40, 60, and 80°C) and three inlet mass flow rates (0.25, 0.50, and 0.75 g/s). Furthermore, PEC-based processes are tested under two light settings (600 and 1200 W/m2). These results are compared to the thermodynamic model outputs. Parametric studies are run by varying the operating temperature (0°C–80°C), inlet mass flow rate (0.01 g/s–1 g/s), and environmental temperature (0°C–40°C). The present experimental results show that PEC-chloralkali has the highest H2 production rate compared to other processes at all temperatures and flow rates. Under 1200 W/m2 irradiation, at 20°C and 0.75 g/s, Process 4 has a H2 production rate of 3.48 mg/h.27% and 26% are the highest energy and exergy efficiencies reached at 0.75 g/s inlet mass flow rate and 20°C operating temperature and under 600 W/m2 irradiation. A multi-objective optimization study is performed to find the decision variables for the highest possible production, efficiencies, and lowest possible exergy destruction, cost, and emissions. These parameters are 1°C operating temperature, 1.4 g/s inlet flow rate, 6 m2 total photoactive area, and 0°C environmental temperature. And overall exergy efficiency is 30%, and H2 production cost and emissions are 9.67 USD/kg H2 and 7.39 kg CO2/kg H2.