Assessing the scalability of low conductivity substrates for photo-electrodesviamodelling of resistive losses

Abstract

When scaling up photo-electrochemical processes to larger areas than conventionally studied in the laboratory, substrate performance must be taken into consideration and in this work, a methodology to assess this via an uncomplicated 2 dimensional model is outlined. It highlights that for F-doped SnO2 (FTO), which is ubiquitously used for metal oxide photoanodes, substrate performance becomes significant for moderately sized electrodes (5 cm) under no solar concentration for state of the art Fe2O3 thin films. It is demonstrated that when the process is intensified via solar concentration, current losses become quickly limiting. Methodologies to reduce the impact of substrate ohmic losses are discussed and a new strategy is proposed. Due to the nature of the photo-electrode current-potential relationship, operation at a higher potential where the photo-current saturates (before the dark current is observed) will lead to a minimum in current loss due to substrate performance. Crucially, this work outlines an additional challenge in scaling up photo-electrodes based on low conductivity substrates, and establishes that such challenges are not insurmountable.

Demonstration of a 50 cm2 BiVO4 tandem photoelectrochemical-photovoltaic water splitting device

“…Our calculations fall in line with what has been previously reported for the resistive losses caused by large area FTO substrates. 36 This problem has also been encountered in photovoltaic cells, where the sheet resistance of FTO used as a top contact layer is too high for efficient current collection. 37 This is typically resolved by depositing highly conductive metallic busbars on the front contact of the PV cells.…”

Mitigating voltage losses in photoelectrochemical cell scale-up

“…21 The signicant loss of efficiency has been attributed not to the scale-up of the light absorber material (i.e., BiVO 4 ) itself, but more to the ohmic losses and mass-transport (proton/hydroxyl ions) limitations. Several modeling studies have also investigated some of these aspects (substrate losses, ionic drop, mass transfer), [24][25][26][27][28] but the overall quantication of the various loss mechanisms related to scale-up has not been reported. This is important in order to propose and implement appropriate (photo)electrochemical engineering and design strategies in order to overcome the scale-up related losses.…”

Effect of the ambient conditions on the operation of a large-area integrated photovoltaic-electrolyser

“…11,[16][17][18][19] Although there are no abrupt changes and the transport losses increase continuously with increasing device size, different transport losses, perhaps coincidentally, signicantly affect device operation when the distances reach the centimetre scale, matching the limit of the laboratory-scale. 11,16,[19][20][21][22][23] Especially losses in electrolyte for large devices are underestimated by measurements of small samples. 16 In principle, large areas could be covered by replicating a small device numerous times, but there may be practical limitations to how large such a base unit should be at least.…”