Yongpeng Liu

Yongpeng Liu is currently a final year Ph.D. student in Chemistry and Chemical Engineering at École Polytechnique Fédérale de Lausanne (EPFL) under the supervision of Prof. Kevin Sivula and Dr. Néstor Guijarro. His doctoral research consists of solution-processed photoelectrodes (metals oxides and chalcopyrite) and operando spectroelectrochemistry. So far, some of his doctoral works have been published in 21 peer-reviewed scientific journals (8 first/co-first author, 5 second author, and 1 corresponding author) and have been presented in 15 conferences (8 oral presentations and 10 poster presentations). He obtained his master’s degree with distinction in Nanoscience and Nanotechnology at the University of Glasgow in 2016. He studied Materials Science and Engineering in Huazhong University of Science and Technology from 2011 to 2015.

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Bulk Heterojunction Organic Semiconductor Photoanodes: Tuning Energy Levels to Optimize Electron Injection

Han-Hee Cho, Nestor Guijarro Carratala, Yongpeng Liu, Juan Manuel Moreno Naranjo, Barbara Alexandra Primera Darwich, Arvindh Sekar, Kevin Sivula, Liang Yao, Jun Ho Yum

The use of a bulk heterojunction of organic semiconductors to drive photoelectrochemical water splitting is an emerging trend; however, the optimum energy levels of the donor and acceptor have not been established for photoanode operation with respect to electrolyte pH. Herein, we prepare a set of donor polymers and non-fullerene acceptors with varying energy levels to probe the effect of photogenerated electron injection into a SnO(2)(-)based substrate under sacrificial photo-oxidation conditions. Photocurrent density (for sacrificial oxidation) up to 4.1 mA cm(-2) was observed at 1.23 V vs reversible hydrogen electrode in optimized photoanodes. Moreover, we establish that a lower lying donor polymer leads to improved performance due to both improved exciton separation and better charge collection. Similarly, lower-lying acceptors also give photoanodes with higher photocurrent density but with a later photocurrent onset potential and a narrower range of pH for good operation due to the Nernstian behavior of the SnO2, which leads to a smaller driving force for electron injection at high pH.

AMER CHEMICAL SOC2022

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A semiconducting polymer bulk heterojunction photoanode for solar water oxidation

Florent Alexandre Boudoire, Han-Hee Cho, Nestor Guijarro Carratala, Yongpeng Liu, Arvindh Sekar, Kevin Sivula, Rebekah Anne Wells, Liang Yao, Jun Ho Yum

Organic semiconductors hold promise to enable scalable, low-cost and high-performance artificial photosynthesis. However, the performance of systems based on organic semiconductors for light-driven water oxidation have remained poor compared with inorganic semiconductors. Herein, we demonstrate an all-polymer bulk heterojunction organic semiconductor photoanode for solar water oxidation. By engineering the photoanode interlayers we gain important insights into critical factors (surface roughness and charge extraction efficiency) to increase the operational stability, which reaches above 3 h with a 1-Sun photocurrent density, J(ph), of >3 mA cm(-2) at 1.23 V versus the reversible hydrogen electrode for the sacrificial oxidation of Na2SO3 at pH 9. Optimizing the coupling to an oxygen evolution catalyst yields O-2 production with J(ph) > 2 mA cm(-2) at 1.23 V versus the reversible hydrogen electrode (100% Faradaic efficiency and a quantum efficiency up to 27% with 610 nm illumination), demonstrating improved stability (>= 1 mA cm(-2) for over 30 min of continuous operation) compared with previous organic photoanodes. Conductive polymers are attractive materials for the construction of photoelectrodes in the context of artificial photosynthesis, although their performance is still limited. Now, an organic semiconductor photoanode for water oxidation is presented, which provides high photocurrent density for over 30 minutes.

NATURE RESEARCH2021

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Defect engineered nanostructured LaFeO3 photoanodes for improved activity in solar water oxidation

Nestor Guijarro Carratala, Yongpeng Liu, Mounir Driss Mensi, Xavier Pereira Da Costa, Kevin Sivula, Liang Yao

LaFeO3 (LFO) is recognized as a candidate material for solar water oxidation, but its photoelectrochemical response remains modest and stagnant. With the aim of advancing LFO photoanodes for the oxygen evolution reaction (OER), here, a nanorod array-type electrode combined with defect and surface engineering protocols has been demonstrated, delivering a benchmark performance of 0.4 mA cm−2 at 1.23 V vs. RHE with an onset potential below 0.55 V vs. RHE. It was found that oxygen defects activated the surface towards OER, while NiFeOx coating suppressed surface recombination. It was discovered, however, that the performance was limited by rapid (nanosecond timescale) bulk recombination, as well as the ultrashort hole diffusion length (

2021

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