Solar Water Oxidation by a Visible‐Light‐Responsive Tantalum/Nitrogen‐Codoped Rutile Titania Anode for Photoelectrochemical Water Splitting and Carbon Dioxide Fixation

Abstract

Non‐oxide materials such as oxynitrides are good candidates as photoanodes for visible‐light‐driven water oxidation, but most of them suffer from oxidative degradation by photogenerated holes, resulting in low stability. Herein we developed a photoanode using a visible‐light‐responsive TiO2 powder doped with tantalum and nitrogen (TiO2:Ta/N) for water oxidation. The Ta/N codoping enabled a stable anodic photocurrent response attributable to water oxidation under visible‐light irradiation. Surface modification of the TiO2:Ta/N anode with RuOx species further facilitated water oxidation catalysis, achieving stable O2 evolution over 5 h of operation with no sign of deactivation. Operando XAFS measurements revealed an important function of the RuOx species as a collector of photogenerated holes in TiO2:Ta/N, facilitating the photoelectrochemical water oxidation. Visible‐light‐driven H2 evolution and solar‐driven CO2 reduction into CO were both achieved by using water as an electron donor in photoelectrochemical cells with the TiO2:Ta/N photoanode coupled to a Pt cathode and a Ru(II)–Re(I) binuclear complex photocathode, respectively.

Enhancement of Photocatalytic Activity for Hydrogen Production by Surface Modification of Pt‐TiO2 Nanoparticles with a Double Layer of Photosensitizers

“…To construct highly active Z‐scheme water‐splitting photocatalysts, the charge separation efficiency in the DSP must be improved, and the selective recognition of oxidized or reduced mediators is important for achieving one‐way electron transfer from the oxygen evolution photocatalyst to hydrogen evolution photocatalyst. Although most studies of DSPs have been conducted in the presence of sacrificial electron donators to promote the water‐splitting half reaction, [30–35] there have been several reports concerning water reduction or overall water splitting in the presence of redox‐reversible electron mediators [36, 37] . In 1993, Mallouk and co‐workers achieved an apparent quantum yield (AQY) of 0.3 % using a Ru II photosensitizer (PS) immobilized on the surface of a water reduction catalyst, Pt/H x K 4− x Nb 6 O 17 , with iodide as a redox‐reversible electron donor [38] .…”

“…Althoughm ost studies of DSPsh ave been conducted in the presence of sacrificial electron donators to promote the water-splittingh alf reaction, [30][31][32][33][34][35] there have been several reports concerning water reduction or overallw ater splitting in the presence of redox-reversible electron mediators. [36,37] In 1993,M allouk and co-workers achieveda na pparentq uantum yield (AQY) of 0.3 %u sing aR u II photosensitizer (PS) immobilized on the surface of aw ater reduction catalyst, Pt/ H x K 4Àx Nb 6 O 17 ,w ith iodide as ar edox-reversible electron donor. [38] In 2013, Abe et al reported overall water splitting (AQY = 0.05 %) using coumarin derivatives( NKX-2677) immobilized on Pt/H x K 4Àx Nb 6 O 17 as aw ater reductionD SP coupled with an O 2 evolution photocatalyst comprising IrO 2 -Pt/WO 3 and iodide redox mediator.…”

Structure‐Activity Relationship in a Cobalt Aluminate Nanoparticle Cocatalyst with a Graphitic Carbon Nitride Photocatalyst for Visible‐Light Water Oxidation

“…Further research will be needed for elucidation of the reaction mechanism (e. g., investigation of the change in the valence state and local structure of Co 2 + and Al 3 + during the water oxidation reaction). We believe that in situ (or operando) XAFS measurement [41] is one of the candidates to clarify it, and will be performed as part of our future works.…”

Selective CO2 reduction into formate using Ln–Ta oxynitrides combined with a binuclear Ru(II) complex under visible light

“…Combining the RuRu' with a visible-light-absorbing semiconductor that has strong oxidation ability enables one to accomplish CO 2 reduction even with the use of a weak electron donor [7]. In some photoelectrochemical systems constructed from a similar binuclear metal complex and a semiconductor, sacrificial reagent-free CO 2 reduction has been achieved [9][10][11]. As these hybrid systems are based on the combination of photocatalysis of semiconductors and molecules, it is important to develop both of the two in harmony.…”