Integrated Photo-Electrochemical Solar Fuel Generators under Concentrated Irradiation

Abstract

Concentrating solar irradiation for use in integrated photo-electrochemical devices potentially provides an economically competitive pathway for hydrogen generation, even with partial use of rare material components. Heat transfer and thermal management are crucial in devices operating under large irradiation concentrations. With dedicated thermal management, detailed 2-dimensional multiphysics modeling predicts high performance. Two competing operational parameter spaces are observed: i) thermal effects enhance performance in the zone of low operational current density, and ii) mass transport limits dominate in the zone of high operational current density (saturation current of the electrolyzer component). These competing effects lead to tradeoffs between device efficiency and hydrogen evolution rate, quantified using Pareto frontiers. Smart thermal management -only possible through integrated device design -helps in achieving efficient and low cost production of solar fuels, and can further alleviate degradation-related performance decreases over the lifetime of the device. For example, at an irradiation concentration of 707, a 12% degradation in STH efficiency of a Si-based device is compensated by a seven-fold increase in the water mass flow rate. Integrated photo-electrochemical device designs combined with smart thermal management prove to be a practical and economically feasible approach to solar fuel processing, and provide a pathway to circumvent limitations imposed by materials. The solar energy received on earth's surface, capable of meeting mankind's current and future energy demands, 1-4 can be directly converted into electricity using photovoltaic cells. However, electricity is difficult and costly to store, and considerable losses are accrued when attempting to distribute it over long distances. This problem can be circumvented by directly converting the photon energy into fuels. The simplest reaction considered is the electrolysis of water to produce hydrogen. Hydrogen can become a complementing energy carrier, and can be used as an energy-rich reagent for the exothermic formation of methane, methanol, or hydrocarbons using atmospheric CO 2 as a carbon feedstock. To realize this goal, practical means for sustainable hydrogen production are needed. Today more than 95% of global hydrogen production is based on steam reforming of fossil fuels.5 A promising sustainable approach to hydrogen production is solar driven, using integrated photo-electrochemical (IPEC) pathways. An IPEC device is defined as a device in which an area-matched photoabsorber and electrocatalyst are in direct contact. We propose an integrated photo-electrochemical device design, shown in Fig. 1. This device profits from the exclusion of direct semiconductor-electrolyte interfaces prone to interface degradation issues, and limits the transmission losses occurring in completely unintegrated, externally wired photovoltaic plus electroyzer systems. The design incorporates an electronic conductor for the transfer of charge carriers f...

Kilowatt-scale solar hydrogen production system using a concentrated integrated photoelectrochemical device

“…Additionally, this direct-integration device architecture has also been applied to developing technologies such as alkaline anion exchange membrane electrolysis 7 . These experimental demonstrations, along with the previous modelling 27,30,32,33 , demonstrate the synergistic effect of heat integration of the photoelectrochemical device. However, these studies also established the need for careful thermal management to advantageously benefit from such thermal integration, highlighting the integrated device design, selected operating conditions and the observation of material limits (for example, PV, PEM) as key issues.…”

Integrated Photo-Electrochemical Solar Fuel Generators under Concentrated Irradiation

“…A more detailed analysis and the quantitative/qualitative benefits of smart thermal management for the integrated design of IPECs will be detailed in follow-up studies. 41 …”

In situ observation of pH change during water splitting in neutral pH conditions: impact of natural convection driven by buoyancy effects

“…[1][2][3][4][5][6][7][8] Heat transfer from the semiconductor to the electrolyte solution will help to reduce photovoltage losses, especially for temperature-sensitive materials such as Si-and III/V-based semiconductors. [8][9][10][11] Conversely, higher temperatures may improve charge carrier transport when metal oxide semiconductors with polaronic properties are used. [12][13][14][15] This is in contrast to PV-coupled electrolyzers, for which the efficiency has been shown to decrease with increasing operating temperature.…”