A Stand‐Alone Si‐Based Porous Photoelectrochemical Cell

Abstract

Wireless photoelectrochemical (PEC) devices promise easy device fabrication as well as reduced losses. Here, the design and fabrication of a stand‐alone ion exchange material‐embedded, Si membrane‐based, photoelectrochemical cell architecture with micron‐sized pores is shown, to overcome the i) pH gradient formation due to long‐distance ion transport, ii) product crossover, and iii) parasitic light absorption by application of a patterned catalyst. The membrane‐embedded PEC cell with micropores utilizes a triple Si junction cell as the light absorber, and Pt and IrOx as electrocatalysts for the hydrogen evolution reactions and oxygen evolution reactions, respectively. The solar‐to‐hydrogen efficiency of 7% at steady‐state operation, as compared to an unpatterned ηPV of 10.8%, is mainly attributed to absorption losses by the incorporation of the micropores and catalyst microdots. The introduction of the Nafion ion exchange material ensures an intrinsically safe PEC cell, by reducing the total gas crossover to <0.1%, while without a cation exchange membrane, a crossover of >6% is observed. Only in a pure electrolyte of 1 m H2SO4, a pH gradient‐free system is observed thus completely avoiding the build‐up of a counteracting potential.

Stand‐Alone Photoelectrochemical Energy Conversions

“…Adapted with permission. [ 75 ] Copyright 2019, John Wiley and Sons. c) InGaP/GaAs solar cells for the HER with their d) external quantum efficiency measurements under 1 sun illumination.…”

“…Huskens and co‐workers reported a monolithic ion‐exchange material‐embedded PEC cell connected with triple‐junction Si cell as the light absorber, and Pt and IrO x as electrocatalysts for the HER and OER, respectively (Figure 7b). [ 75 ] It is a wireless design and reduces losses due to several wire connections, resulting in an Eff STH of up to 7%. A simulation study revealed that the proton diffusion distance between the cathode and the anode is the key parameter, and the large distance creates a pH gradient that ultimately develops an overpotential.…”

En Route to a Unified Model for Photoelectrochemical Reactor Optimization. II–Geometric Optimization of Perforated Photoelectrodes

“…A more detailed description of existing models was presented in Part I of this extended study (Bedoya-Lora et al, 2017b). • Studies of the spatial distributions of electrode kinetics through: ○ Use of louvered photoelectrodes to minimize product crossover and ohmic losses in neutral and acidic solutions (Haussener et al, 2012;Chen et al, 2014Chen et al, , 2016Jin et al, 2014;Walczak et al, 2015;Singh et al, 2017), ○ Perforating electrodes to minimize ohmic potential losses (Bosserez et al, 2016;Bedoya-Lora et al, 2017b;Hankin et al, 2017;Trompoukis et al, 2018;Vijselaar et al, 2019). • Direct experimental validation of model predictions of current density distributions across planar and perforated photoelectrodes in an up-scaled reactor (Ong et al, 2011;Carver et al, 2012;Hankin et al, 2017).…”

“…Regarding perforated electrodes, minimization of inhomogeneities in spatial distributions of current densities between opposing electroactive surfaces in systems 2 and 3 by means of macro-or microscopic perforations has been proposed conceptually (Orazem and Newman, 1984a;1984b), validated experimentally, and modelled for wired monopolar PECs (Hankin et al, 2017) and wireless bipolar IPECs (Bosserez et al, 2016;Trompoukis et al, 2018;Vijselaar et al, 2019). Example structures of the perforations, as well as their purpose, are illustrated in Figure 1.…”

“…The model can be used to design composite photoelectrodes, fabricated with µm resolution and, for given conditions and photoelectrode properties, optimize geometries of perforations, which cause loss of photoabsorber area, but homogenize spatial distributions of reaction rates. In principle, perforations can be achieved by using an expanded mesh substrate for photoelectrode deposition (Hankin et al, 2017) or, alternatively, laser ablation (Bosserez et al, 2016) or deep reactive etching (Vijselaar et al, 2019) may be used to introduce perforations into pre-formed (photo-)electrodes.…”