Experimental Demonstration of Integrated Photoelectrochemical Hydrogen Generation Utilizing Concentrated Irradiation

Abstract

Integrated PEC devices, which are composed of a traditional photovoltaics (PV) component closely incorporated with an electrolyzer (EC) component, allow to circumvent some of the challenges imposed by solid-liquid interfaces in traditional PEC devices while operating at higher efficiencies than externally wired (non-integrated) PV plus EC devices. Concentrating the solar irradiation and using it in integrated PEC devices (CPEC) has the potential to provide an economically competitive hydrogen generation pathway even when partially utilizing components made of rare materials [1]. An economically competitive CPEC device design point in terms of irradiation and current concentration was predicted using our holistic design guidance methodology discussed in [1]. For this design point, we then detailed the design of a lab scale CPEC prototype utilizing the design guidelines formulated based on our 2D coupled multi-physics CPEC model presented in [2] which uses finite element and finite volume methods to predict the performance of the device. The model accounted for charge generation and transport in the multi-junction solar cell and the components of the integrated electrolyzer (polymeric electrolyte and solid electrode), electrochemical reaction at the catalytic sites, fluid flow and species transport in the channels delivering the reactant (water) and removing the products (hydrogen and oxygen), and radiation absorption and heat transfer in all components. The detailed device design is depicted in figure 1.a. The prototype incorporates Ga0.51In0.49P-GaAs dual junction as the PV component working at an irradiance concentration of 800. The LRESE high flux solar simulator is used for achieving large irradiation concentrations (C=500-1000) [3]. The prototype incorporates smart thermal management strategies allowing solar to hydrogen conversion efficiencies as high as 20% [2]. Large irradiation concentration reduces the H2 cost estimated to be around 1.5 $/kg of H2 at the exit of the device [1]. The prototype incorporates a PV area of 4 cm2 and an electrolyser area of 25 cm2. The input power of the device is 272 W with the estimated H2 production power of 54.4 W. The CPEC device is expected to generate hydrogen at a rate of 1.4 g/hour. The prototype demonstrates an efficient and cost effective way of solar hydrogen processing and provides data for the 2D multi-physics model validation. The model proves to be an accurate tool for the design of integrated CPEC cells working at elevated temperatures and, in combination with the experiments, highlights that the smart thermal management can help in achieving low cost production of solar fuel at fast rates.