Dan Ren

Exfoliated 2D Layered and Nonlayered Metal Phosphorous Trichalcogenides Nanosheets as Promising Electrocatalysts for CO2 Reduction

Michael Graetzel, Yelin Hu, Yunfei Jiao, Dan Ren, Chen Shen, Bing Wu, Hong Zhang

Two-dimensional (2D) materials catalysts provide an atomic-scale view on a fascinating arena for understanding the mechanism of electrocatalytic carbon dioxide reduction (CO2 ECR). Here, we successfully exfoliated both layered and nonlayered ultra-thin metal phosphorous trichalcogenides (MPCh(3)) nanosheets via wet grinding exfoliation (WGE), and systematically investigated the mechanism of MPCh(3) as catalysts for CO2 ECR. Unlike the layered CoPS3 and NiPS3 nanosheets, the active Sn atoms tend to be exposed on the surfaces of nonlayered SnPS3 nanosheets. Correspondingly, the nonlayered SnPS3 nanosheets exhibit clearly improved catalytic activity, showing formic acid selectivity up to 31.6 % with -7.51 mA cm(-2) at -0.65 V vs. RHE. The enhanced catalytic performance can be attributed to the formation of HCOO* via the first proton-electron pair addition on the SnPS3 surface. These results provide a new avenue to understand the novel CO2 ECR mechanism of Sn-based and MPCh(3)-based catalysts.

WILEY-V C H VERLAG GMBH2023

A universal co-solvent dilution strategy enables facile and cost-effective fabrication of perovskite photovoltaics

Paramvir Ahlawat, Masaud Hassan S Almalki, Viacheslav Bolnykh, Ulf Anders Hagfeldt, Anurag Krishna, Linfeng Pan, Dan Ren, Ursula Röthlisberger, Sandy Sanchez Alonso, Tzu-Sen Su, Narges Yaghoobi Nia, Shaik Mohammed Zakeeruddin, Hong Zhang

Cost management and toxic waste generation are two key issues that must be addressed before the commercialization of perovskite optoelectronic devices. We report a ground-breaking strategy for eco-friendly and cost-effective fabrication of highly efficient perovskitesolar cells. This strategy involves the usage of a high volatility co-solvent, which dilutesperovskite precursors to a lower concentration (1.4 M) solution. More than 70% of toxicwaste and material cost can be reduced. Mechanistic insights reveal ultra-rapid evaporationof the co-solvent together with beneficial alteration of the precursor colloidal chemistryupon dilution with co-solvent, which in-situ studies and theoretical simulations confirm.The co-solvent tuned precursor colloidal properties also contribute to the enhancement ofthe stability of precursor solution, which extends its processing window thus minimizing thewaste. This strategy is universally successful across different perovskite compositions, andscales from small devices to large-scale modules using industrial spin-coating, potentiallyeasing the lab-to-fab translation of perovskite technologies.

2022

Regulated CO adsorption by the electrode with OH− repulsive property for enhancing C–C coupling

Jing Gao, Michael Graetzel, Jingshan Luo, Dan Ren, Mingkui Wang, Xiaoyu Zhang, Qixing Zhang

Electrochemical CO2 reduction driven by renewable electricity is one of the promising strategies to store sustainable energy as fuels. However, the selectivity of value-added multi-carbon products remains poor for further application of this process. Here, we regulate CO adsorption by forming a Nafion layer on the copper (Cu) electrode that is repulsive to OH−, contributing to enhanced selectivity of CO2 reduction to C2+ products with the suppression of C1 products. The operando Raman spectroscopy indicates that the local OH− would adsorb on part of active sites and decrease the adsorption of CO. Therefore, the electrode with repulsive to OH− can adjust the concentration of OH−, leading to the increased adsorption of CO and enhanced C–C coupling. This work shows that electrode design could be an effective strategy for improving the selectivity of CO2 reduction to multi-carbon products.

2022

Revisiting the Impact of Morphology and Oxidation State of Cu on CO2 Reduction Using Electrochemical Flow Cell

Jing Gao, Dan Ren, Shaik Mohammed Zakeeruddin

Electroreduction of carbon dioxide (CO2) in a flow electrolyzer represents a promising carbon-neutral technology with efficient production of valuable chemicals. In this work, the catalytic performance of polycrystalline copper (Cu), Cu2O-derived copper (O(I)D-Cu), and CuO-derived copper (O(II)D-Cu) toward CO2 reduction is unraveled in a custom-designed flow cell. A peak Faradaic efficiency of >70% and a production rate of ca. -250 mA cm(-2) toward C2+ products have been achieved on all the catalysts. In contrast to previous studies that reported a propensity for C2+ products on OD-Cu in conventional H-cells, the selectivity and activity of ethylene-dominated C2+ products are quite similar on the three types of catalysts at the same current density in our flow reactor. Our analysis also reveals current density to be a critical factor determining the C-C coupling in a flow cell, regardless of Cu catalyst's initial oxidation state and morphology.

AMER CHEMICAL SOC2022

Solar reduction of carbon dioxide on copper-tin electrocatalysts with energy conversion efficiency near 20%

Jing Gao, Jun Li, Yuhang Liu, Dan Ren, Meng Xia, Shaik Mohammed Zakeeruddin

Solar-driven carbon dioxide reduction has witnessed a renaissance in the past decades, but the system suffers from low reaction rates. Here the authors develop a copper/tin-oxide electrocatalyst, achieving a new benchmark solar-to-CO energy conversion efficiency in a flow electrolyzer. Copper catalysts modified with tin have been demonstrated to be selective for the electroreduction of carbon dioxide to carbon monoxide. However, such catalysts require the precise control of tin loading amount. Here, we develop a copper/tin-oxide catalyst with dominant tin oxide surface being formed via a spontaneous exchange reaction between sputtered tin and copper oxide. Even though the surface of this catalyst is tin-rich, it achieves an excellent performance towards carbon monoxide production in a flow cell. This contrasts with copper/tin-oxide prepared via atomic layer deposition since it yields selectivity towards carbon monoxide only on a copper-rich surface. Mechanism studies reveal that the tin sites on the tin-rich copper/tin-oxide surface achieve a suitable binding with adsorbed carbon monoxide under the presence of copper. Powered by a triple-junction solar cell, the copper/tin-oxide based electrolyzer sets a new benchmark solar-to-chemical energy conversion efficiency of 19.9 percent with a Faradaic efficiency of 98.9 percent towards carbon monoxide under simulated standard air mass 1.5 global illumination.

NATURE PORTFOLIO2022

Solar Water Splitting Using Earth-Abundant Electrocatalysts Driven by High-Efficiency Perovskite Solar Cells

Michael Graetzel, Dan Ren, Shaik Mohammed Zakeeruddin, Hong Zhang

Hydrogen is considered as the "holy grail" for the energy community. One of the most promising strategies to produce hydrogen is to split water using renewable energy such as solar radiation. The abundance of water and solar energy enables the potential of scaling-up of this new technology, if suitable electrocatalysts and solar cells are developed. In this work, a series of materials made of earth-abundant elements was investigated for hydrogen evolution or oxygen evolution reaction. Among the developed catalysts, MoS2 and NiFe showed the best activities for proton reduction and water oxidation, respectively. These catalysts were further integrated into an alkaline electrolyzer, which delivered a current density of 10 mA cm(-2) at a cell voltage of 1.9 V for water splitting. Using two in-series-connected perovskite solar cells (PSCs) as a power source, a remarkable solar-to-hydrogen conversion efficiency of 12.67 % was achieved in an alkaline electrolyzer with a partial current density of 10.3 mA cm(-2) for hydrogen production. The usage of earth-abundant catalysts in this study, together with the employment of low-cost perovskite light absorber, shows the potential of scaling up this type of photovoltaic electrolyzer for sustainable hydrogen production.

WILEY-V C H VERLAG GMBH2022

Benzylammonium‐Mediated Formamidinium Lead Iodide Perovskite Phase Stabilization for Photovoltaics

Anwar Qasem M Alanazi, Masaud Hassan S Almalki, Felix Thomas Eickemeyer, David Lyndon Emsley, Michael Graetzel, Ulf Anders Hagfeldt, Dominik Józef Kubicki, Jovana Milic, Aditya Mishra, Dan Ren, Zaiwei Wang, Shaik Mohammed Zakeeruddin, Hong Zhang

There is an ongoing surge of interest in the use of formamidinium (FA) lead iodide perovskites in photovoltaics due to their exceptional optoelectronic properties. However, thermodynamic instability of the desired cubic perovskite (α-FAPbI3) phase at ambient conditions leads to the formation of a yellow non-perovskite (δ-FAPbI3) phase that compromises its utility. A stable α-FAPbI3 perovskite phase is achieved by employing benzylammonium iodide (BzI) and the microscopic structure is elucidated by using solid-state NMR spectroscopy and X-ray scattering measurements. Perovskite solar cells based on the FAPbI3(BzI)0.25 composition achieve power conversion efficiencies exceeding 20%, which is accompanied by enhanced shelf-life and operational stability, maintaining 80% of the performance after one year at ambient conditions.

2021

Carbazol-phenyl-phenothiazine-based sensitizers for dye-sensitized solar cells

Yi Ding, Felix Thomas Eickemeyer, Wei Huang, Yunfei Jiao, Lukas Pfeifer, Dan Ren, Zhongjin Shen, Shaik Mohammed Zakeeruddin

Heteroaromatic units are commonly used as pi-spacers for sensitizers in dye-sensitized solar cells (DSSCs). Here, we investigated the influence of the pi-spacer on the photophysical properties, electrochemical properties and photovoltaic performance of carbazol-phenyl functionalized phenothiazine donor based organic dyes, i.e., CPPC-No (without a pi-spacer), CPPC-Th (thiophene as the pi-spacer), CPPC-Fu (furane as the pi-spacer), CPPC-Ph (phenyl as the pi-spacer) and CPPC-Py (pyridine as the pi-spacer). The solar to electric power conversion efficiency (PCE) achieved with these dyes strongly depends on the type of pi-spacer, increasing in the order of CPPC-Ph < No < Py < Th < Fu. The width of the absorption band and the photocurrent density increased with the electron richness of the pi-spacer. Theoretical calculations indicated that the planar molecular configuration of CPPC-Fu promotes the intramolecular charge transfer process. As a result, the CPPC-Fu based device showed a PCE of 7.4% under one sunlight illumination. The dyes using thiophene and pyridine as pi-spacers showed slightly lower performance, however, still significantly higher than the PCE achieved with the control compound lacking a pi-spacer. By contrast, introducing a phenyl group as the pi-spacer led to a decrease in device efficiency. These results give deeper insight into the effect of different pi-spacers on DSSC performance, showing the importance of molecular engineering in developing high efficiency organic dyes.

ROYAL SOC CHEMISTRY2021

Gold-in-copper at low *CO coverage enables efficient electromethanation of CO2

Michael Graetzel, Yang Li, Jun Li, Pengfei Ou, Dan Ren, Xiaoyan Wang, Zishuai Wang, Ying Wang, Yi Xu

The renewable-electricity-powered CO2 electroreduction reaction provides a promising means to store intermittent renewable energy in the form of valuable chemicals and dispatchable fuels. Renewable methane produced using CO2 electroreduction attracts interest due to the established global distribution network; however, present-day efficiencies and activities remain below those required for practical application. Here we exploit the fact that the suppression of *CO dimerization and hydrogen evolution promotes methane selectivity: we reason that the introduction of Au in Cu favors *CO protonation vs. C-C coupling under low *CO coverage and weakens the *H adsorption energy of the surface, leading to a reduction in hydrogen evolution. We construct experimentally a suite of Au-Cu catalysts and control *CO availability by regulating CO2 concentration and reaction rate. This strategy leads to a 1.6x improvement in the methane:H-2 selectivity ratio compared to the best prior reports operating above 100mAcm(-2). We as a result achieve a CO2-to-methane Faradaic efficiency (FE) of (562)% at a production rate of (112 +/- 4) mA cm(-2). The electroreduction of CO2 offers a promising approach to produce carbon-neutral methane using renewable electricity. This study shows that the introduction of Au in Cu enables selective methane production from CO2 by regulating *CO availability.

NATURE RESEARCH2021

Dan Ren

Exfoliated 2D Layered and Nonlayered Metal Phosphorous Trichalcogenides Nanosheets as Promising Electrocatalysts for CO2 Reduction

A universal co-solvent dilution strategy enables facile and cost-effective fabrication of perovskite photovoltaics

Regulated CO adsorption by the electrode with OH− repulsive property for enhancing C–C coupling

Revisiting the Impact of Morphology and Oxidation State of Cu on CO2 Reduction Using Electrochemical Flow Cell

Solar reduction of carbon dioxide on copper-tin electrocatalysts with energy conversion efficiency near 20%

Solar Water Splitting Using Earth-Abundant Electrocatalysts Driven by High-Efficiency Perovskite Solar Cells

Transparency and Morphology Control of Cu2O Photocathodes via an in Situ Electroconversion

Benzylammonium‐Mediated Formamidinium Lead Iodide Perovskite Phase Stabilization for Photovoltaics

Carbazol-phenyl-phenothiazine-based sensitizers for dye-sensitized solar cells

Gold-in-copper at low *CO coverage enables efficient electromethanation of CO2

Solar Water Splitting Using Earth-Abundant Electrocatalysts Driven by High-Efficiency Perovskite Solar Cells

Exfoliated 2D Layered and Nonlayered Metal Phosphorous Trichalcogenides Nanosheets as Promising Electrocatalysts for CO2 Reduction

A universal co-solvent dilution strategy enables facile and cost-effective fabrication of perovskite photovoltaics

Revisiting the Impact of Morphology and Oxidation State of Cu on CO2 Reduction Using Electrochemical Flow Cell

Regulated CO adsorption by the electrode with OH− repulsive property for enhancing C–C coupling

Solar reduction of carbon dioxide on copper-tin electrocatalysts with energy conversion efficiency near 20%

Transparency and Morphology Control of Cu2O Photocathodes via an in Situ Electroconversion

Benzylammonium‐Mediated Formamidinium Lead Iodide Perovskite Phase Stabilization for Photovoltaics

Carbazol-phenyl-phenothiazine-based sensitizers for dye-sensitized solar cells

Gold-in-copper at low *CO coverage enables efficient electromethanation of CO2