Gradient tantalum-doped hematite homojunction photoanode improves both photocurrents and turn-on voltage for solar water splitting

Abstract

Hematite has a great potential as a photoanode for photoelectrochemical (PEC) water splitting by converting solar energy into hydrogen fuels, but the solar-to-hydrogen conversion efficiency of state-of-the-art hematite photoelectrodes are still far below the values required for practical hydrogen production. Here, we report a core-shell formation of gradient tantalum-doped hematite homojunction nanorods by combination of hydrothermal regrowth strategy and hybrid microwave annealing, which enhances the photocurrent density and reduces the turn-on voltage simultaneously. The unusual bi-functional effects originate from the passivation of the surface states and intrinsic built-in electric field by the homojunction formation. The additional driving force provided by the field can effectively suppress charge–carrier recombination both in the bulk and on the surface of hematite, especially at lower potentials. Moreover, the synthesized homojunction shows a remarkable synergy with NiFe(OH)x cocatalyst with significant additional improvements of photocurrent density and cathodic shift of turn-on voltage. The work has nicely demonstrated multiple collaborative strategies of gradient doping, homojunction formation, and cocatalyst modification, and the concept could shed light on designing and constructing the efficient nanostructures of semiconductor photoelectrodes in the field of solar energy conversion.

Interface engineering of Ta3N5 thin film photoanode for highly efficient photoelectrochemical water splitting

“…Photoelectrochemical impedance spectroscopy (PEIS) was employed to compare the charge transfer processes between Ta 3 N 5 and In:GaN/Ta 3 N 5 /Mg:GaN photoanodes 14,22 . The PEIS Nyquist plots in Fig.…”

“…Over the past decade, tremendous efforts have been devoted to interface engineering of various semiconductor photoelectrodes (e.g., Si 20,21 , α-Fe 2 O 3 22 , BiVO 4 23 , Cu 2 O 24 ) to improve their efficiency and stability through the passivation of interfacial defects or formation of hetero-/homojunctions. Ideally, the semiconductor thin film light absorbers should be sandwiched by a n-type electron transport layer (ETL) and a p-type hole transport layer (HTL) to achieve efficient charge separation, similar to the "n-i-p" device architecture commonly used in thin-film photovoltaics 25 .…”

Advancing Photoelectrochemical Energy Conversion through Atomic Design of Catalysts

“…[ 138 , 139 ] Recently, heteroatom doping ( Figure 8 a ) has shown great potential in PEC‐driven catalytic reactions. [ 140 , 141 ]…”

Unravelling the impact of Ta doping on the electronic and structural properties of titania: A combined theoretical and experimental approach

“…In recent years, Ta-TiO2 has been investigated for solar cells 18 , water splitting 19 , corrosion resistance 20 , photovoltaics 17 , wastewater treatment 8 , oxygen reduction reaction 21 , and lithium ion batteries 22 . These reports have shown that Ta could be utilised as an effective additive or dopant to increase the catalytic performance of TiO2.…”