A Flexible Web‐Based Approach to Modeling Tandem Photocatalytic Devices

Abstract

There have been several works modeling the optimal band gaps for tandem photocatalytic water splitting devices under different assumptions. Due to the many parameters involved, it is impossible for the authors to consider every conceivable situation. In this work, we have developed a web‐based model (WBM) that allows users to input data such as photoabsorber diode parameters, catalytic losses, ionic losses, light concentration, etc. This program also adds a new parameter that allows one to balance the photon absorption distribution between both photoabsorbers in a tandem device (by thinning the top photoabsorber), thus allowing for a broader range of band gap combinations that can still provide highly efficient devices. While this does not change the overall maximum efficiency point, at certain band gap combinations balancing the photon absorption distribution between photoabsorbers can increase Solar to Hydrogen (STH) efficiency by up to 15% points. An additional feature of the WBM is that it allows users to upload data of a single photoelectrode, and then investigate the optimal matching photoabsorber band gap to maximize tandem device efficiency. This work analyzes some of the best previous experimental photoelectrodes, and quantitatively relates their performance to what would typically be expected via modeling programs.

Performance Limits of Photoelectrochemical CO2 Reduction Based on Known Electrocatalysts and the Case for Two-Electron Reduction Products

“…These assumptions are consistent with our previous work on water splitting 13 , are deliberately conservative so as to be realizable in practice. The electrolyte reported by Chen et al 35 is CO 2 saturated 0.5 M KHCO 3 for which the conductivity is assumed to be 38.8 mS/cm at 298 K and we model ionic resistance with a 0.5 cm effective ionic path length (which is taken to include the resistance of a possible membrane).…”

Beyond Water Splitting: Efficiencies of Photo‐Electrochemical Devices Producing Hydrogen and Valuable Oxidation Products

“…[16,43,44] Using the WBM we have calculated solar-to-chemical/solarto-hydrogen (STC/STH) efficiencies of different devices (for further information see the Supporting Information). The baseline parameters used to model these devices were chosen in agreement with previous work by Seger et al [32] (see Table 2 and Table S1 and Figure S1, Supporting Information). For BrER and ClER the parameters were modified to account for changes in overpotential and ionic conductivity.…”

“…The STH efficiency calculations were performed using the WBM. [32] a,b) Calculated using kinetic parameters as shown in Table 2, allowing light absorption by a thin water film. c) Current matching by top cell absorber thinning is allowed to mitigate limitations by the bottom cell.…”

“…[9,24,25] Since all of the aforementioned reactions are simple 2e − oxidation reactions with minimal overpotential, losses should be less important than encountered in water oxidation. [26,27] PEC systems for water splitting [17,[28][29][30][31][32][33] have been extensively modeled, and to less extent PEC systems for CO 2 reduction have been as well. [34,35] To the best of our knowledge, in-depth modeling of halide oxidation, or oxidation of water to H 2 O 2 , has yet to be published.…”

“…We discuss the effect of the thermodynamic potential and kinetics of the different oxidation reactions on the solar-to-hydrogen (STH) efficiencies of PEC devices and point out how new catalysts for partial oxidation of water to H 2 O 2 will increase PEC efficiencies. Utilizing state-of-the-art modeling approaches provided by a JavaScript, web based model (WBM) developed by Seger et al, [32] we will demonstrate that bromine, chlorine, and hydrogen peroxide based STH conversion efficiencies are high, and PEC technology may be economically viable.The oxidation reactions considered in this study are summarized in Equations (1) Of all these oxidation reactions, only the bromine evolution reaction (BrER, Equation (1)) is thermodynamically favored over the oxygen evolution reaction (OER, Equation (4) …”