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1. Unbiased solar H2 production with current density up to 23 mA cm2 by Swiss-cheese black Si coupled with wastewater bioanode

   Lu, L. ; Vakki, W. ; Aguiar, A. J. ; Xiao, C.X. ; Hurst, K. ; Fairchild, M. ; Chen, X. ; Yang, F. ; Gu, J.* ( January 2019 , Energy & environmental science)

   Unbiased photoelectrochemical hydrogen production with high efficiency and durability is highly desired for solar energy storage. Here, we report a microbial photoelectrochemical (MPEC) system that demonstrated superior performance when equipped with bioanodes and black silicon photocathode with a unique ‘‘Swiss-cheese’’ interface. The MPEC utilizes the chemical energy embedded in wastewater organics to boost solar H2 production, which overcomes barriers on anode H2O oxidation. Without any bias, the MPEC generates a record photocurrent (up to 23 mA cm2) and retains prolonged stability for over 90 hours with high Faradaic efficiency (96–99%). The calculated turnover number for MoSx catalyst during a 90 h period is 495 471 with an average frequency of 1.53 s1 . The system replaced pure water on the anode with actual wastewater and achieved waste organic removal up to 16 kg COD m2 photocathode per day. Cost credits from concurrent wastewater treatment and low-cost design make photoelectrochemical H2 production practical for the first time 

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2. Electrical decoupling of microbial electrochemical reactions enables spontaneous H 2 evolution

   https://doi.org/10.1039/C9EE02571E  

   Chen, Xi ; Lobo, Fernanda Leite ; Bian, Yanhong ; Lu, Lu ; Chen, Xiaowen ; Tucker, Melvin P. ; Wang, Yuxi ; Ren, Zhiyong Jason ( February 2020 , Energy & Environmental Science)

   Hydrogen evolution is not a spontaneous reaction, so current electrochemical H 2 systems either require an external power supply or use complex photocathodes. We present in this study that by using electrical decoupling, H 2 can be produced spontaneously from wastewater. A power management system (PMS) circuit was deployed to decouple bioanode organic oxidation from abiotic cathode proton reduction in the same electrolyte. The special PMS consisted of a boost converter and an electromagnetic transformer, which harvested energy from the anode followed by voltage magnification from 0.35 V to 2.2–2.5 V, enabling in situ H 2 evolution for over 96 h without consuming any external energy. This proof-of-concept demonstrated a cathode faradaic efficiency of 91.3% and a maximum overall H 2 conversion efficiency of 28.9%. This approach allows true self-sustaining wastewater to H 2 evolution, and the system performance can be improved via the PMS and reactor optimization. 

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3. Photorechargeable High Voltage Redox Battery Enabled by Ta 3 N 5 and GaN/Si Dual‐Photoelectrode

   https://doi.org/10.1002/adma.201700312  

   Cheng, Qingmei ; Fan, Weiqiang ; He, Yumin ; Ma, Peiyan ; Vanka, Srinivas ; Fan, Shizhao ; Mi, Zetian ; Wang, Dunwei ( May 2017 , Advanced Materials)

   Solar rechargeable battery combines the advantages of photoelectrochemical devices and batteries and has emerged as an attractive alternative to artificial photosynthesis for large‐scale solar energy harvesting and storage. Due to the low photovoltages by the photoelectrodes, however, most previous demonstrations of unassisted photocharge have been realized on systems with low open circuit potentials (<0.8 V). In response to this critical challenge, here it is shown that the combined photovoltages exceeding 1.4 V can be obtained using a Ta₃N₅nanotube photoanode and a GaN nanowire/Si photocathode with high photocurrents (>5 mA cm^–2). The photoelectrode system makes it possible to operate a 1.2 V alkaline anthraquinone/ferrocyanide redox battery with a high ideal solar‐to‐chemical conversion efficiency of 3.0% without externally applied potentials. Importantly, the photocharged battery is successfully discharged with a high voltage output.

    

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4. >10% solar-to-hydrogen efficiency unassisted water splitting on ALD-protected silicon heterojunction solar cells

   https://doi.org/10.1039/c9se00110g  

   Tan, Chor Seng ; Kemp, Kyle W. ; Braun, Michael R. ; Meng, Andrew C. ; Tan, Wanliang ; Chidsey, Chris E. ; Ma, Wen ; Moghadam, Farhad ; McIntyre, Paul C. ( May 2019 , Sustainable Energy & Fuels)

   Solar water splitting using photoelectrochemical cells (PEC's) is a promising pathway toward clean and sustainable storage of renewable energy. Practical realization of solar-driven synthesis of hydrogen and oxygen integrating light absorption and electrolysis of water has been challenging because of (1) the limited stability of good photovoltaic materials under the required electrochemical conditions, and (2) photovoltaic efficiency losses due to light absorption by catalysts, the electrolyte, and generated bubbles, or reflection at their various interfaces. Herein, we evaluate a novel integrated solar water splitting architecture using efficient silicon heterojunction photovoltaic cells that avoids such losses and exhibits a solar-to-hydrogen (STH) efficiency in excess of 10%. Series-connected silicon Heterojunction with Intrinsic Thin layer (HIT) cells generate sufficient photovoltage for unassisted water splitting, with one of the cells acting as the photocathode. Platinum is deposited on the back (dark) junction of this HIT cell as the catalyst for the hydrogen evolution reaction (HER). The photocathode is protected from corrosion by a TiO 2 layer deposited by atomic layer deposition (ALD) interposed between the HIT cell and the Pt, enabling stable operation for >120 hours. Combined with oxygen evolution reaction (OER) catalysts deposited on a porous metal dark anode, these PEC's achieve stable water splitting with a record high STH efficiency for an integrated silicon photosynthesis device. 

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5. Scalable Core–Shell MoS 2 /Sb 2 Se 3 Nanorod Array Photocathodes for Enhanced Photoelectrochemical Water Splitting

   https://doi.org/10.1002/solr.201900442  

   Guo, Liping ; Shinde, Pravin S. ; Ma, Yanxiao ; Li, Lin ; Pan, Shanlin ; Yan, Feng ( November 2019 , Solar RRL)

   Photoelectrochemical (PEC) hydrogen generation is a promising solar energy harvesting technique to address the concerns about the ongoing energy crisis. Antimony selenide (Sb₂Se₃) with van der Waals‐bonded quasi‐1D (Q1D) nanoribbons, for instance, (Sb₄Se₆)_n, has attracted considerable interest as a light absorber with Earth‐abundant elements, suitable bandgap, and a desired sunlight absorption coefficient. By tuning its anisotropic growth behavior, it is possible to achieve Sb₂Se₃films with nanostructured morphologies that can improve the light absorption and photogenerated charge carrier separation, eventually boosting the PEC water‐splitting performance. Herein, high‐quality Sb₂Se₃films with nanorod (NR) array surface morphologies are synthesized by a low‐cost, high‐yield, and scalable close‐spaced sublimation technique. By sputtering a nonprecious and scalable crystalline molybdenum sulfide (MoS₂) film as a cocatalyst and a protective layer on Sb₂Se₃NR arrays, the fabricated core–shell structured MoS₂/Sb₂Se₃NR PEC devices can achieve a photocurrent density as high as −10 mA cm⁻²at 0 V_RHEin a buffered near‐neutral solution (pH 6.5) under a standard simulated air mass 1.5 solar illumination. The scalable manufacturing of nanostructured MoS₂/Sb₂Se₃NR array thin‐film photocathode electrodes for efficient PEC water splitting to generate solar fuel is demonstrated.

    

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