Novel Strategies to Optimize Photocatalytic Hydrogen Production Systems

Data:2020-09-18  |  【 A  A  A 】  |  【Print】 【Close

The research team led by Prof. Lingyu Piao from the National Center for Nanoscience and Technology (NCNST) made a progress in photocatalytic H2 production. These findings were published in Nano Energy (2020, 67, 104287)Nano Today (DOI: https:// doi.org/ 10.1016/ j.nantod.2020.100968) and Angew. Chem. Int. Ed. (DOI: 10.1002/ anie.202009633).

Up to now, H2 production mainly relies on coal and natural gas reforming in industry, which aggravates the consumption of non-renewable energy and environmental pollution. Due to solar energy is a renewable, inexhaustible and clean energy (~4×1020 J/h), photocatalytic H2 production using solar energy is one of the most desired methods to solve the energy and environmental problems. Based on the merits of solar and hydrogen energy, Prof. Piao’s group developed two strategies to achieve highly effective and stable photocatalytic H2 production: water splitting and formic acid (FA) dehydrogenation. Besides, they proposed a rational evaluation method for photocatalytic H2 production.

H2 production from water can be achieved through two approaches: (i) photocatalytic overall water splitting (POWS) (2H2O→2H2 + O2); (ii) photocatalytic partial water splitting (PPWS) (2H2O + sacrificial reagent→2H2 + oxidized sacrificial reagent products). Over the past decades, POWS is the most attractive route but is extremely challenging due to low photocatalytic efficiency, potential reverse reactions, and costly separation issues with the produced H2/O2 mixture. Based on the previous work of Piao’s group (Nano Energy 2017, 41, 488-493; Appl. Catal B: Environ 2018, 220, 471-476), they firstly proposed a new photocatalytic water splitting route: photocatalytic intermediate water splitting (PIWS) (2H2O→H2 + H2O2). The significant advantages of PIWS include: (1) PIWS is a more kinetically feasible two-electron reaction. (2) The back-reaction of H2 and O2 was significantly inhibited and the conversion efficiency was further enhanced. (3) PIWS generates more high value products of H2 and H2O2. (4) PIWS is a simple and cost-effective approach. Since the products are H2 gas and H2O2 liquid, they are automatically separated without using any separation facility. Therefore, PIWS holds a great potential for practical applications. This work was published in Nano Energy (2020, 67, 104287). 

The storage and transport of hydrogen are challenges in achieving successful hydrogen economy. FA has attracted considerable attention as a promising hydrogen storage material with its low toxicity, low cost, and high stability. Based on the previous work of Piao’s group (Joule 2018, 2, 549-557), they firstly discovered the catalytic role of H2O for photocatalytic formic acid (FA) dehydrogenation form both theoretical and experimental aspects. The activation energy of photocatalytic FA dehydrogenation can be apparently decreased with a 2~4-fold efficiency increase in photocatalytic H2 production over various photocatalysts systems with the assistance of H2O. This work (Nano Today, 2020, DOI: https:// doi.org/ 10.1016/ j.nantod. 2020.100968) shed light on the pathway for photocatalytic H2 production via FA dehydrogenation and demonstrated H2O should no longer just be considered as a solvent or dispersion medium.

Over the past decades, various photocatalysts have been developed and great progress has been achieved in the field of solar-driven photocatalytic water splitting. However, the lack of an accurate and comprehensive evaluation method greatly hinders the meaningful comparison between different systems and becomes a serious impediment for its development. Based on it, Prof. Piao’s group propose preliminary suggestions from aspects of quantum yields, solar to hydrogen conversion efficiency, catalyst mass and experimental conditions, aiming to help stimulate discussion in the research community and accomplish a widely accepted and authoritative evaluation system to assess the photocatalyst performance. This work was published in Angew. Chem. Int. Ed. (2020, DOI: 10.1002/ anie. 202009633).

These works were financially supported by National Natural Science Foundation of China, and the Strategic Priority Research Program of Chinese Academy of Sciences.


 

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