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

Abstract

Mitigation of ohmic losses and mass transport limitations enables a large area BiVO4-based water splitting device with a solar-to-hydrogen efficiency of 2.1%.

Mitigating voltage losses in photoelectrochemical cell scale-up

“…With increasing inlet velocity, the replenishment and transport of protons close to the anode and cathode surface, respectively, are promoted. This is in agreement with the "restricted" electrolyte volume effect recently demonstrated in an experimental study by Ahmet et al 21 At an inlet velocity of 4 cm s À1 , the maximum pH difference is limited to $0.6 ( Fig. 4d), which corresponds to a voltage loss of only $40 mV.…”

“…46,47 Photocurrent improvements on 50 cm 2 BiVO 4 photoelectrodes have also been demonstrated by depositing conducting nickel lines on top of the FTO substrates. 21 Decreasing d contact to less than 1 cm will further reduce V ohmic,substrate . However, at the same time, a larger portion of the transmitted light will be blocked (see Fig.…”

“…Most reported devices have an area of smaller than 1 cm 2 , and only a handful demonstrated areas larger than 10 cm 2 . 2,[19][20][21][22][23] Moreover, these large-area devices tend to deliver much lower STH efficiency (by up to a factor of $5) as compared to their small-area equivalent. 2 For example, it was recently reported that while small-area (0.24 cm 2 ) BiVO 4 -based tandem device delivers STH efficiency of $6%, the large-area (50 cm 2 ) equivalent is only capable of delivering an STH efficiency of $2%.…”

“…2 For example, it was recently reported that while small-area (0.24 cm 2 ) BiVO 4 -based tandem device delivers STH efficiency of $6%, the large-area (50 cm 2 ) equivalent is only capable of delivering an STH efficiency of $2%. 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.…”

“…In such a conguration, hydrodynamic ow alone is sufficient to separate the products and ensure safe operation without the use of conventional membranes. 29,30 Since it has been shown that the voltage losses associated with scale-up are not due to additional potential drop within the light absorbers, 21 only dark electrochemical reactions are taken into consideration here. For our analysis to be valid, the resistance of the semiconductor layer itself should therefore be negligible and the deposition at large area should still result in homogenous lms.…”