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Observation of 4^th-order water oxidation kinetics by time-resolved photovoltage spectroscopy.

ABSTRACT: Artificial photo-driven water oxidation has been proposed over half a century through a four-charge involved multiple-step oxygen evolution process. However, the knowledge of the intrinsic activity, such as the rate-law of the water oxidation reactions, has been inadequately studied. Up to date, the highest order reported is the third one under photoelectrochemical condition. In this work, we identified the fourth-order charge decay reactions on hematite by using a time-resolved surface photovoltage probe technique. A theoretical turnover frequency (TOF) > 100 nm^-2·s^-1 can be expected for O₂ molecules when the hole density >0.1 nm^-2. This work demonstrates a facile and robust method to investigate the high-order reaction kinetics. More excitingly, this research built the bridge between the rate-law, rate-determining step, and energy barrier of intermediates.

SUBMITTER: Yang X

PROVIDER: S-EPMC8661549 | biostudies-literature | 2021 Dec

REPOSITORIES: biostudies-literature

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Observation of 4<sup>th</sup>-order water oxidation kinetics by time-resolved photovoltage spectroscopy.

Yang Xiaogang X Zheng Zhi Z Hu Jundie J Qu Jiafu J Ma Dekun D Li Jingsha J Guo Chunxian C Li Chang Ming CM

iScience 20211126 12

Artificial photo-driven water oxidation has been proposed over half a century through a four-charge involved multiple-step oxygen evolution process. However, the knowledge of the intrinsic activity, such as the rate-law of the water oxidation reactions, has been inadequately studied. Up to date, the highest order reported is the third one under photoelectrochemical condition. In this work, we identified the fourth-order charge decay reactions on hematite by using a time-resolved surface photovol ...[more]

PMID: 34934920

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Project description:As a vital process for solar fuel synthesis, water oxidation remains a challenging reaction to perform using durable and cost-effective systems. Despite decades of intense research, our understanding of the detailed processes involved is still limited, particularly under photochemical conditions. Recent research has shown that the overall kinetics of water oxidation by a molecular dyad depends on the coordination between photocharge generation and the subsequent chemical steps. This work explores similar effects of heterogeneous solar water oxidation systems. By varying a key variable, the reaction temperature, we discovered distinctly different behaviors on two model systems, TiO2 and Fe2O3. TiO2 exhibited a monotonically increasing water oxidation performance with rising temperature across the entire applied potential range, between 0.1 and 1.5 V vs the reversible hydrogen electrode (RHE). In contrast, Fe2O3 showed increased performance with increasing temperature at high applied potentials (>1.2 V vs RHE) but decreased performance at low applied potentials (<1.2 V vs RHE). This decrease in performance with temperature on Fe2O3 was attributed to an increased level of electron-hole recombination, as confirmed by intensity-modulated photocurrent spectroscopy (IMPS). The origin of the differing temperature dependences on TiO2 and Fe2O3 was further ascribed to their different surface chemical kinetics. These results highlight the chemical nature of charge recombination in photoelectrochemical (PEC) systems, where surface electrons recombine with holes stored in surface chemical species. They also indicate that PEC kinetics are not constrained by a single rate-determining chemical step, highlighting the importance of an integrated approach to studying such systems. Moreover, the results suggest that for practical solar water splitting devices higher temperatures are not always beneficial for reaction rates, especially under low driving force conditions.

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Observation of 4^th-order water oxidation kinetics by time-resolved photovoltage spectroscopy.

Publications

Observation of 4<sup>th</sup>-order water oxidation kinetics by time-resolved photovoltage spectroscopy.

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Observation of 4th-order water oxidation kinetics by time-resolved photovoltage spectroscopy.

Publications

Observation of 4<sup>th</sup>-order water oxidation kinetics by time-resolved photovoltage spectroscopy.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

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Observation of 4^th-order water oxidation kinetics by time-resolved photovoltage spectroscopy.