Effects of a SnO₂ hole blocking layer in a BiVO₄-based photoanode on photoelectrocatalytic water oxidation

Abstract

The Material properties of BiVO4 are modified via coupling with a SnO2 buffer layer inserted between BiVO4 and a FTO substrate.

Atomic Layer Deposition of Space‐Efficient SnO2 Underlayers for BiVO4 Host–Guest Architectures for Photoassisted Water Splitting

“…However, holes generated in BiVO 4 neart he electron-rich FTO can undergo recombination and reduce the quantum efficiency.F TO-absorber interfaces are known to broadly promote recombination for diverse PEC materials, [19,[37][38][39][40][41] suggestingt hat the defects from deliberate fluorine incorporation are recombination sites. Previous reports utilized undoped SnO 2 as an underlayer for BiVO 4 where optimal thicknesses were approximately 80 nm, [2,21] and thinner SnO 2 underlayers did not efficiently inhibit recombination. Common synthetic routesf or SnO 2 ,s uch as spray pyrolysis, result in nonconformal underlayers with relatively high carrier concentrations (10 19 -10 21 cm À3 ;s ee the Supporting Information, Ta bleS1).…”

“…Tino xide is ap opular underlayerm aterial for BiVO 4 ,a cting as ah ole-blocking layer typicallyo ptimizeda t 65-80 nm. [2,21] Such thick underlayers,h owever,c onsumep recious pore volume from the overall 3D host-guest design. The efficacy of low carrier density SnO 2 underlayers were investigated for BiVO 4 PEC performance.…”

“…materials like BiVO 4 ,t he underlayer is sometimes called ah ole blockingl ayer or a" hole mirror." [6,[19][20][21][22][23][24][25] Previous works have commonlyutilized tin oxide (SnO 2 ) [2, 14, 29-32, 19, 21-23, 25-28] and tungsten oxide (WO 3 ), [3,26,33] where SnO 2 is perhaps the most studied underlayer material for BiVO 4 .O ther materials that have been used as interfacial layers in BiVO 4 photoanodes include TiO 2 , [34,35] Lu 2 O 3 , [20] and GaO x N 1-x ; [36] SnO 2 was selected for this study based on its suitable band alignment relative to BiVO 4 , stability, low cost, and as-yet unexplored investigation as a BiVO 4 underlayer using atomic layer deposition (ALD). Popular synthetic methods forS nO 2 ,s uch as spray pyrolysis, yield optimal PEC performance with 65-80nmo fu nderlayer thickness.…”

“…Popular synthetic methods forS nO 2 ,s uch as spray pyrolysis, yield optimal PEC performance with 65-80nmo fu nderlayer thickness. [2,21] With such al arge film thickness, clearlym ore is at play than rectification. The optimal underlayer will (1) fully cover the host interface, preventing access to recombination sites located in the FTO, (2) not provide an ew set of defects that promote recombination, and (3) have minimal thickness to limit the resistancef or electron transport to the electrical contact.T he optimal underlayer thickness for different synthesis routes is of minor importance for flat compact films;h owever,i tp oses as ignificant limitation for practical use in 3D host-guest architectures with limited free-volume.…”

Recent Advances in Bismuth‐Based Nanomaterials for Photoelectrochemical Water Splitting

“…Ag/AgCl BiOI nanoplates [163] solvothermalZnO nanorods 0.5 m Na 2 SO 4 0.2 mA cm À2 at 1.2 V vs. Ag/AgCl BiOI nanoplates [65] spray pyrolysis depositionnone 0.25 m NaI in MeCN 0.9 mA cm À2 at 0.4 V vs. Ag/AgCl BiOI nanoflakes [69] electrodepositionAu nanoparticles0 .5 m Na 2 SO 4 3.6 mA cm À2 at 0V vs. RHE BiVO 4 ultrathinfilm [83] modified sol-gel SnO 2 /Au on polydimethylsiloxane 0.5 m phosphate buffer1.37mAcm À2 at 1.23Vvs. RHE BiVO 4 film [164] modified metal-organicdecomposition SnO 2 0.5 m phosphate buffer 0.95mAcm À2 at 1.23Vvs. RHE BiVO 4 film [160] spray pyrolysis Co-Pi and Wd oping0 .5 m K 2 SO 4 in phosphate buffer 2.3 mA cm À2 at 1.23V vs. RHE BiVO 4 island [143] spin coating WO 3 and TiO 2 0.1 m Na 2 SO 4 4.2 mA cm À2 at 1.23V vs. RHE BiVO 4 island [165] Co-magnetron sputtering Mo 0.5 m Na 2 SO 4 with 0.1 m phosphate buffer 1.2 mA cm À2 at 1.23V vs. RHE BiVO 4 shell [166] drop casting SnO 2 :Sb phosphate bufferwith 1 m Na 2 SO 4 3.9 mA cm À2 at 0.6 V vs. RHE BiVO 4 core-shell [132] electrodepositionWO 3 and Co-Pi potassium phosphate buffer6.722 mA cm À2 at 1.23Vvs.…”