Effects of photo-generated gas bubbles on the performance of tandem photoelectrochemical reactors for hydrogen production

How do bubbles affect light absorption in photoelectrodes for solar water splitting?

“…Fig. 1 presents photographs of typical bubble-covered Si or Pt photocathodes in (a) horizontal 11 or (b) vertical orientations 12 showing significant fraction of the photoelectrode area covered with bubbles. Fig.…”

“…17,18 The curvature of bubbles and the refractive index mismatch at the electrolyte/bubble interface can lead to reflection, refraction, and total internal reflection causing back-scattering of incident photons and significant redistribution of the incident light intensity on the photoelectrode surface. 11,12 These optical effects reduce the photocurrent density generated in the photoelectrode, and ultimately, the efficiency of a photoelectrochemical (PEC) cell. The latter is of utmost importance for the commercial viability and large-scale deployment of this technology.…”

“…Very few studies have analyzed the optical effects of bubbles on the performance of vertical or horizontal photoelectrodes. 2,11,12,19,20 Holmes-Gentle et al 19 conducted experiments to study the optical losses due to a rising plume of O 2 gas bubbles evolving from a transparent vertical electrode consisting of a glass slide of surface area 15 × 15 mm 2 coated with fluorine-doped tin oxide (FTO) and immersed in an aqueous solution of 1 M NaOH. Collimated light was incident normally onto the electrode surface and its normal-hemispherical transmittance was recorded in the presence of bubbles using an integrating sphere.…”

“…Njoka et al 12 characterized the behavior of O 2 and H 2 gas bubbles on the surface of vertically-oriented Pt photoelectrodes by capturing macroscopic images to understand their effect on the performance of a tandem photoelectrochemical cell subject to normally incident radiation. The authors observed that H 2 bubbles tended to grow independently from one another, remained attached to the photoelectrode, and accumulated at its surface for longer periods of time compared to O 2 bubbles which tended to coalesce and rise rapidly.…”

Releasing the Bubbles: Nanotopographical Electrocatalyst Design for Efficient Photoelectrochemical Hydrogen Production in Microgravity Environment

“…[ 21 ] Recently, gas bubble formation has also become the focus of several photoelectrochemical device studies for terrestrial applications. Decelerated gas bubble desorption from the electrode surface causes light reflection from bubbles adhering to the electrode surface, [ 22 , 23 , 24 ] the blockage of catalytically active sites, [ 22 , 24 ] and limited substrate and product transfer to and from the electrode surface. [ 24 ] These are all factors which significantly lower the overall device output.…”