Pristine GaFeO₃ Photoanodes with Surface Charge Transfer Efficiency of Almost Unity at 1.23 V for Photoelectrochemical Water Splitting

Abstract

Oxide-based photoelectrodes commonly generate deep trap states associated with various intrinsic defects such as vacancies, antisites, and dislocations, limiting their photoelectrochemical properties. Herein, it is reported that rhombohedral GaFeO 3 (GFO) thin-film photoanodes exhibit defect-inactive features, which manifest themselves by negligible trap-states-associated charge recombination losses during photoelectrochemical water splitting. Unlike conventional defect-tolerant semiconductors, the origin of the defect-inactivity in GFO is the strongly preferred antisite formation, suppressing the generation of other defects that act as deep traps. In addition, defect-inactive GFO films possess really appropriate oxygen vacancy concentration for the oxygen evolution reaction (OER). As a result, the as-prepared GFO films achieve the surface charge transfer efficiency (𝜼 surface ) of 95.1% for photoelectrochemical water splitting at 1.23 V versus RHE without any further modification, which is the highest 𝜼 surface reported of any pristine inorganic photoanodes. The onset potential toward the OER remarkably coincides with the flat band potential of 0.43 V versus RHE. This work not only demonstrates a new benchmark for the surface charge transfer yields of pristine metal oxides for solar water splitting but also enriches the arguments for defect tolerance and highlights the importance of rational tuning of oxygen vacancies.

Insight of the State for Deliberately Introduced A-Site Defect in Nanofibrous LaFeO3 for Boosting Artificial Photosynthesis of CH3OH

“…As observed from the transient photocurrent responses spectra (Figure a), all of the samples exhibited a fast response upon illumination, followed by a relaxation to a quasi-steady-state value. The overshoot of photocurrents in the transient photocurrent responses spectra was the evidence of the surface recombination. , Although there was clear evidence of photogenerated carriers recombined, La 0.9 FeO 3−δ exhibited higher photocurrent density compared with La 1.0 FeO 3−δ , which meant that the La 0.9 FeO 3−δ generated more carriers under photoexcitation. , It could be seen from the EIS data (Figure b) that the Nyquist plot semicircle of La 0.9 FeO 3−δ was smaller than La 1.0 FeO 3−δ , indicating that the introduction of La 3+ deficiency and smaller diameter nanofiber structures might reduce the charge transfer resistance …”

“…47,48 Although there was clear evidence of photogenerated carriers recombined, La 0.9 FeO 3−δ exhibited higher photocurrent density compared with La 1.0 FeO 3−δ , which meant that the La 0.9 FeO 3−δ generated more carriers under photoexcitation. 49,50 It could be seen from the EIS data (Figure 7b) that the Nyquist plot semicircle of La 0.9 FeO 3−δ was smaller than La 1.0 FeO 3−δ , indicating that the introduction of La 3+ deficiency and smaller diameter nanofiber structures might reduce the charge transfer resistance. 51 As shown in Figure 7c, La 0.9 FeO 3−δ exhibited a higher transient photocurrent density, which indicated that more photogenerated carriers were generated after photoexcitation.…”

Multifunctional Role of Ag‐Substitution in Enhancing the Photoelectrochemical Properties of LaFeO3 Photocathodes

“…[19,20] In this case, an approximated fitting was implemented according to previous studies, where the peak in the middle is assigned to Fe 3 + , and the other two peaks at low and high binding energies are associated with Fe 2 + and Fe 4 + , respectively. [14,21] The main characteristic of the O 1s region is located at 529.0 eV, which points to the metal bound normal oxygen (O L ). The other components correspond to hydroxyl species (À OH), undercoordinated oxygen (O À )/carbonate compounds (CO 3 2À ), and adsorbed water (H 2 O ads ).…”

Improving the photovoltage of Cu2O photocathodes with dual buffer layers

“…Hydrogen is clean and has a high energy density, these properties make it a key candidate for use as a sustainable fuel 4,5 . A transition to sustainable hydrogen fuel will contribute greatly toward the development of a low carbon circular economy and achieving net-zero emissions 6 . Photoelectrochemical (PEC) water splitting can solve the problem of solar energy harvest and storage 7 by converting intermittent solar energy into hydrogen fuel 8,9 , which has received great attention in the past decades 10,11 .…”