Momentum-resolved electronic structure of LaTiO2N photocatalysts by resonant Soft-X-ray ARPES

Abstract

Oxynitrides are promising materials for visible light-driven water splitting. However, limited information regarding their electron-momentum resolved electronic structure exists. Here, with the advantage of the enhanced probing depth and chemical state specificity of soft-X-ray ARPES, we determine the electronic structure of the photocatalyst oxynitride LaTiO2N and monitor its evolution as a consequence of the oxygen evolution reaction. After the photoelectrochemical reactions, we observe a partial loss of Ti- and La-N 2p states, distortions surrounding the local environment of titanium atoms and, unexpectedly, an indication of an electron accumulation layer at or near the surface, which may be connected with either a large density of metallic surface states or downward band bending. The distortions and defects associated with the titanium 3d states lead to the trapping of electrons and charge recombination, which is a major limitation for the oxynitride LaTiO2N. The presence of an accumulation layer and its evolution suggests complex mechanisms of the photoelectrochemical reaction, especially in cases where co-catalysts or passivation layers are used.

Single-Crystalline LaTiO2N Nanosheets with Regulated Defects for Photocatalytic Overall Water Splitting under Visible Light up to 600 nm

“…Moreover, the broad PL emission can be further deconvolved into two peaks centered at approximately 673 (1.84 eV) and 793 nm (1.56 eV). The peak at 673 nm can be assigned to Ti 3+ -mediated emissions as Ti 3+ species generally form the shallow donor levels slightly below the conduction band. ,,,, This peak in LaTiO 2 N–N is weaker compared to that in LaTiO 2 N–S, which is in line with their different levels of Ti 3+ concentration. The peak at 793 nm, however, is from the deep-level defect emissions and is probably mediated by anion defects that concomitantly formed with Ti 3+ defects .…”

“…Previous studies have suggested that the defects play a pivotal role in governing the photocatalytic performance of LaTiO 2 N. − ,− The types of defects in LaTiO 2 N, their locations, energy states, concentrations, etc., correlate intrinsically with the behavior of photocarriers (e – and h + ). For instance, a variety of crystal defects have been identified in conventionally prepared LaTiO 2 N, including stacking faults, coherent low-angle domain boundaries, oxygen-rich planes, twin domains, grain boundaries, surface reconstruction layers, ,, various point defects [e.g., Ti 3+ , oxygen vacancies (V O ), nitrogen vacancies (V N ), and oxygen at nitrogen sites (O N )], ,,,− etc. These defects, particularly when they are located in the bulk, are detrimental to photocatalytic activity as they can retard the movement of photocarriers and trigger unproductive photocarrier recombination .…”

Unraveling the Role of Orbital Interaction in the Electrochemical HER of the Trimetallic AgAuCu Nanobowl Catalyst

“…7,8 Water is electrolyzed using two half-cell processes, the HER and the OER, which take place at the cathode and anode, respectively. 9 Multiple electron-coupled transfer processes were used in these reactions, which require highly active catalysts to reduce the significant overpotential given by electrocatalysis. 10 An excellent catalyst must operate admirably in terms of the HER with the lowest overpotential and highest stability.…”

“…There are numerous applications of electrocatalysis in technological chemical processes such as organic synthesis, sensors, fuel cells, Li-ion batteries, nitrogen reduction reactions (NRR), CO 2 reduction, etc. Among them, the most promising, environmentally friendly, and environmentally sustainable method of producing hydrogen and oxygen is known as the electrocatalytic water-splitting reaction. , Water is electrolyzed using two half-cell processes, the HER and the OER, which take place at the cathode and anode, respectively . Multiple electron-coupled transfer processes were used in these reactions, which require highly active catalysts to reduce the significant overpotential given by electrocatalysis .…”