@article {1111, title = {Development of a Photoelectrochemically Self-Improving Si/GaN Photocathode for Efficient and Durable H2 Production}, journal = {Nature Materials}, year = {2021}, month = {04/2021}, pages = {1-6}, doi = {10.1038/s41563-021-00965-w}, url = {https://doi.org/10.1038/s41563-021-00965-w}, author = {Guosong Zeng and Tuan Anh Pham and Srinivas Vanka and Guiji Liu and Chengyu Song and Jason K. Cooper and Zetian Mi and Tadashi Ogitsu and Francesca M. Toma} } @article {1084, title = {Dependence of interface energetics and kinetics on catalyst loading in a photoelectrochemical system}, journal = {Nano Research}, year = {2019}, abstract = {

Published on March 11th, 2019. Solar hydrogen production by the photoelectrochemical method promises a means to store solar energy. While it is generally understood that the process is highly sensitive to the nature of the interface between the semiconductor and the electrolyte, a detailed understanding of this interface is still missing. For instance, few prior studies have established a clear relationship between the interface energetics and the catalyst loading amount. Here we aim to study this relationship on a prototypical Si-based photoelectrochemical system. Two types of interfaces were examined, one with GaN nanowires as a protection layer and one without. It was found that when GaN was present, higher Pt loading (\> 0.1 μg/cm2) led to not only better water reduction (and, hence, hydrogen evolution) kinetics but also more favorable interface energetics for greater photovoltages. In the absence of the protection layer, by stark contrast, increased Pt loading exhibited no measurable influence on the interface energetics, and the main difference was observed only in the hydrogen evolution kinetics. The study sheds new light on the importance of interface engineering for further improvement of photoelectrochemical systems, especially concerning the role of catalysts and protection layers.

}, issn = {1998-0000}, doi = {10.1007/s12274-019-2346-3}, url = {https://doi.org/10.1007/s12274-019-2346-3}, author = {Yumin He and Srinivas Vanka and Tianyue Gao and Da He and Jeremy Espano and Yanyan Zhao and Qi Dong and Chaochao Lang and Yongjie Wang and Thomas W. Hamann and Zetian Mi and Dunwei Wang} } @article {1081, title = {An In0.42Ga0.58N tunnel junction nanowire photocathode monolithically integrated on a nonplanar Si wafer}, journal = {Nano Energy}, volume = {57}, year = {2019}, pages = {405-413}, abstract = {

Published on March 1st, 2019. Group III-nitride semiconductors exhibit many ideal characteristics for solar water splitting, including a tunable energy bandgap across nearly the entire solar spectrum and suitable band edge positions for water oxidation and proton reduction under visible and near-infrared light irradiation. To date, however, the best reported energy conversion efficiency for III-nitride semiconductor photocathodes is still below 1\%. Here we report on the demonstration of a relatively efficient p-type In0.42Ga0.58N photocathode, which is monolithically integrated on an n-type nonplanar Si wafer through a GaN nanowire tunnel junction. The open pillar design, together with the nonplanar Si wafer can significantly maximize light trapping, whereas the tunnel junction reduces the interfacial resistance and enhances the extraction of photo-generated electrons. In addition, photodeposited Pt nanoparticles on InGaN nanowire surfaces significantly improve the cathodic performance. The nanowire photocathode exhibits a photocurrent density of 12.3 mA cm-2 at 0 V vs. RHE and an onset potential of 0.79 V vs. RHE under AM 1.5 G one-sun illumination. The maximum applied bias photon-to-current efficiency reaches 4\% at ~0.52 V vs. RHE, which is one order of magnitude higher than the previously reported values for III-nitride photocathodes. Significantly, no performance degradation was measured for over 30 h solar water splitting with a steady photocurrent density ~12 mA cm-2 without using any extra surface protection, which is attributed to the spontaneous formation of N-terminated surfaces of InGaN nanowires to protect against photocorrosion.

}, issn = {2211-2855}, doi = {10.1016/j.nanoen.2018.12.067}, url = {http://www.sciencedirect.com/science/article/pii/S2211285518309807}, author = {Yongjie Wang and Srinivas Vanka and Jiseok Gim and Yuanpeng Wu and Ronglei Fan and Yazhou Zhang and Jinwen Shi and Mingrong Shen and Robert Hovden and Zetian Mi} } @article {1093, title = {A Single-Junction Cathodic Approach for Stable Unassisted Solar Water Splitting}, journal = {Joule}, year = {2019}, abstract = {

Published in August 2019.

}, issn = {25424351}, doi = {10.1016/j.joule.2019.07.022}, url = {https://linkinghub.elsevier.com/retrieve/pii/S2542435119303666}, author = {Yongjie Wang and Yuanpeng Wu and Jonathan Schwartz and Suk Hyun Sung and Robert Hovden and Zetian Mi} } @article {1085, title = {Gallium nitride nanowire as a linker of molybdenum sulfides and silicon for photoelectrocatalytic water splitting}, journal = {Nature Communications}, volume = {9}, year = {2018}, month = {09/2018}, pages = {3856}, abstract = {

Published on September 21st, 2018. Sunlight-harvesting materials require the clean integration of light-absorbing and catalytic components to be efficient. Here, authors link silicon photoelectrodes and molybdenum sulfide catalysts with defect-free gallium nitride nanowire to improve photoelectrochemical hydrogen evolution.

}, issn = {2041-1723}, doi = {10.1038/s41467-018-06140-1}, url = {https://www.nature.com/articles/s41467-018-06140-1}, author = {Baowen Zhou and Xianghua Kong and Srinivas Vanka and Sheng Chu and Pegah Ghamari and Yichen Wang and Nick Pant and Ishiang Shih and Hong Guo and Zetian Mi} } @article {1086, title = {High Efficiency Si Photocathode Protected by Multifunctional GaN Nanostructures}, journal = {Nano Letters}, volume = {18}, year = {2018}, pages = {6530-6537}, abstract = {

Published on October 10th, 2018. Photoelectrochemical water splitting is a clean and environmentally friendly method for solar hydrogen generation. Its practical application, however, has been limited by the poor stability of semiconductor photoelectrodes. In this work, we demonstrate the use of GaN nanostructures as a multifunctional protection layer for an otherwise unstable, low-performance photocathode. The direct integration of GaN nanostructures on n+{\textendash}p Si wafer not only protects Si surface from corrosion but also significantly reduces the charge carrier transfer resistance at the semiconductor/liquid junction, leading to long-term stability (\>100 h) at a large current density (\>35 mA/cm2) under 1 sun illumination. The measured applied bias photon-to-current efficiency of 10.5\% is among the highest values ever reported for a Si photocathode. Given that both Si and GaN are already widely produced in industry, our studies offer a viable path for achieving high-efficiency and highly stable semiconductor photoelectrodes for solar water splitting with proven manufacturability and scalability.

}, issn = {1530-6984}, doi = {10.1021/acs.nanolett.8b03087}, url = {https://doi.org/10.1021/acs.nanolett.8b03087}, author = {Srinivas Vanka and Elisabetta Arca and Shaobo Cheng and Kai Sun and Gianluigi A. Botton and Glenn Teeter and Zetian Mi} } @article {1079, title = {A photochemical diode artificial photosynthesis system for unassisted high efficiency overall pure water splitting}, journal = {Nature Communications}, volume = {9}, year = {2018}, pages = {1707}, issn = {2041-1723}, doi = {10.1038/s41467-018-04067-1}, url = {https://www.nature.com/articles/s41467-018-04067-1}, author = {Faqrul A. Chowdhury and Michel L. Trudeau and Hong Guo and Zetian Mi} } @article {1042, title = {Solar Water Oxidation by an InGaN Nanowire Photoanode with a Bandgap of 1.7 eV}, journal = {ACS Energy Letters}, volume = {3}, year = {2018}, note = {

{\textquoteright}doi: 10.1021/acsenergylett.0c01132\n - I.Am.Hydrogen{\textquoteright} {\textquoteright}\n - jyoungstrom{\textquoteright} {\textquoteright}Jason thinks this is great.\n\ \n - jyoungstrom{\textquoteright} {\textquoteright}\n - estechel{\textquoteright}

}, pages = {307-314}, abstract = {

Published on February 9th, 2018. The performance of overall solar water splitting has been largely limited by the half-reaction of water oxidation. Here, we report a 1.7 eV bandgap InGaN nanowire photoanode for efficient solar water oxidation. It produces a low onset potential of 0.1 V versus a reversible hydrogen electrode (RHE) and a high photocurrent density of 5.2 mA/cm2 at a potential as low as 0.6 V versus RHE. The photoanode yields a half-cell solar energy conversion efficiency up to 3.6\%, a record for a single-photon photoanode to our knowledge. Furthermore, in the presence of hole scavengers, the photocurrent density of the InGaN photoanode reaches 21.2 mA/cm2 at 1.23 V versus RHE, which approaches the theoretical limit for a 1.7 eV InGaN absorber. The InGaN nanowire photoanode may serve as an ideal top cell in a photoelectrochemical tandem device when stacked with a 0.9{\textendash}1.2 eV bandgap bottom cell, which can potentially deliver solar-to-hydrogen efficiency over 25\%.

}, doi = {10.1021/acsenergylett.7b01138}, url = {https://doi.org/10.1021/acsenergylett.7b01138}, author = {Sheng Chu and Srinivas Vanka and Yichen Wang and Jiseok Gim and Yongjie Wang and Yong-Ho Ra and Robert Hovden and Hong Guo and Ishiang Shih and Zetian Mi} }