Lab name: Ren Group

Group leader: Zhifeng Ren

Location: University of Houston

Further information: 
https://mynsm.uh.edu/wiki/pages/
s4p050e/Professor_Zhifeng_Ren.html

Professor Zhifeng Ren.
Professor Zhifeng Ren.
Measured thermal conductivity of BAs in comparison with theoretical calculations and other crystals. Calculated ? versus temperature for BAs (black) and diamond (green) including only three-phonon scattering (dashed lines) and both three- and four-phonon scattering (solid lines). Measured ? for diamond by TDTR (green diamonds). Measured ? for BAs Sample #1 (solid red symbols) and #2 (open red symbols) by TDTR, Sample #3 by FDTR (solid orange star for mean value), steady-state (open blue squares) and lock-in Raman (open brown square) methods, and Sample #5 by the steady-state method (solid blue squares). Also shown are the fits to measured steady-state and TDTR ? for Bas (blue and red solid lines, respectively), and reported measured ? for GaN (21) and GaAs (22) (magenta and purple triangles, respectively). The error bars for the TDTR and FDTR data represent one standard deviation and were obtained via Monte Carlo simulations and derivative matrix-based analysis of uncertainty propagation, respectively (15). The error bars for the steady state and lock-in Raman measurement results were calculated by propagating random errors at 95% confidence and systematic errors (15).
Measured thermal conductivity of BAs in comparison with theoretical calculations and other crystals. Calculated ? versus temperature for BAs (black) and diamond (green) including only three-phonon scattering (dashed lines) and both three- and four-phonon scattering (solid lines). Measured ? for diamond by TDTR (green diamonds). Measured ? for BAs Sample #1 (solid red symbols) and #2 (open red symbols) by TDTR, Sample #3 by FDTR (solid orange star for mean value), steady-state (open blue squares) and lock-in Raman (open brown square) methods, and Sample #5 by the steady-state method (solid blue squares). Also shown are the fits to measured steady-state and TDTR ? for Bas (blue and red solid lines, respectively), and reported measured ? for GaN (21) and GaAs (22) (magenta and purple triangles, respectively). The error bars for the TDTR and FDTR data represent one standard deviation and were obtained via Monte Carlo simulations and derivative matrix-based analysis of uncertainty propagation, respectively (15). The error bars for the steady state and lock-in Raman measurement results were calculated by propagating random errors at 95% confidence and systematic errors (15).

Energy is one of the three basic requirements for life, along with food and water. Zhifeng Ren of the University of Houston has devoted himself to energy-related materials research for the last 30 years.

As the M. D. Anderson Chair Professor in the Department of Physics and the Texas Center on Superconductivity (TcSUH), Ren leads a research group focusing on nanomaterial approaches to high-performance thermoelectrics, solar energy conversion, transparent electrodes, surfactants for oil recovery, carbon nanomaterials, and superconductivity.

Ren received a B.S. from Sichuan Institute of Technology and an M.S. from Huazhong University of Science and Technology, before completing a Ph.D. at the Institute of Physics, Chinese Academy of Sciences, in Beijing. He joined the University of Houston in 2013, following appointments at Boston College and SUNY at Buffalo. As well as authoring many papers, Zhifeng Ren is also Editor-in-Chief of the journal Materials Today Physics, published by Elsevier. He has received many awards and accolades including Outstanding Overseas Chinese Young Investigator in 2005, R&D 100 Award in 2008, and Edith and Peter O’Donnell Award in Science from The Academy of Medicine, Engineering & Science of Texas in 2014.

Zhifeng Ren talked to Materials Today about his current research and future plans.

How long has the lab been running?

We have been at the University of Houston for five and a half years, but were previously located at Boston College for thirteen-and-a-half years.

How many staff makes up the lab?

We have about 10-15 PhD students and 8-12 postdocs from Physics, Chemistry, Mechanical Engineering, Materials Science, Electrical Engineering, Chemical Engineering, and other departments.

What are the major themes of research in your group?

We focus on, but are not limited to, high-performance nanostructured thermoelectrics; novel nanosheets for enhanced oil recovery; highly efficient electrocatalysts for water splitting to generate hydrogen; high thermal conductivity materials such as boron arsenide single crystals, thin films, and devices; flexible transparent electrodes for electronic devices; high temperature superconductors; and carbon nanotubes.

How and why did you come to work in these areas?

All my research areas are energy-related. Energy is one of the three most basic human needs of beings, the other two being water and food.

What facilities and equipment does the lab have?

We have a series of facilities for single crystal growth, thin film deposition, and bulk material synthesis including tube and box furnaces, ball milling machines, hot presses, magnetron sputtering machines, transport measurement systems, and many others.

Do you have a favorite piece of kit or equipment?

Cannot really just name one, since many of them are essential such as ball milling machines and hot press systems, transport measurement systems, and so on.

What do you think has been your most influential work to date?

It is not just a single piece of work but a few that is my most influential. First, as early as in 1995 when I was still at the SUNY Buffalo as a research faculty, I made high-quality Tl2Ba2CuO6 thin films for Tsuei and Kirtley at IBM and van der Marel in Holland, which they used to prove pure d-wave electron pairing symmetry experimentally [10, 11, 12].

Then, in 1998, my group discovered aligned carbon nanotubes [9], which started a ‘gold rush’ worldwide making and studying them. This paper was the most cited paper in materials science for many years and has now been cited for more than 2100 times according to Web of Knowledge.

In 2008, my group together with Gang Chen’s group at Massachusetts Institute of Technology discovered that thermoelectric figure-of-merit can be significantly enhanced using a simple ball milling and hot pressing method to create nanostructured bulk materials [8]. This paper, which has been cited for more than 2600 times and is one of the top five most cited papers in thermoelectrics, opened up a new direction for thermoelectrics.

Very recently, my group together with others, have grown single crystals of BAs of 4 x 2 x 1 mm for the first time to demonstrate thermal conductivity above 1000 W/(m K), second only to diamond [1]. This work will have a profound impact on thermal management and many other fields. In fact, we have also published outstanding results on enhanced oil recovery, hydrogen generation by water splitting, and other topics.  

What is the key to running a successful group?

The key is to have an open mind and create a creative lab environment that lets postdocs and students think freely and have the confidence to try new things, as well as frequent interaction among lab personnel to help them learn from each other. Of course, sufficient funding is the most important thing. 

How do you plan to develop your group in the future?

I have been very lucky over the years, discovering new materials and physical phenomena, which have led to new fields for many others to follow. Since the way we operate the lab is working very well, I will continue in the same way with corrections from time to time whenever they are needed.

Key publications

  1. F. Tian, B. Song, X. Chen, N. K. Ravichandran, Y. Lv, K. Chen, S. Sullivan, J. Kim, Y. Zhou, T.-H. Liu, M. Goni, Z. Ding, J. Sun, G. A. G. U. Gamage, H. Sun, H. Ziyaee, S. Huyan, L. Deng, J. Zhou, A. J. Schmidt, S. Chen, C.-W. Chu, P. Y. Huang, D. Broido, L. Shi, G. Chen, Z. F. Ren,. Unusual High Thermal Conductivity in Boron Arsenide Bulk Crystals. Science 361 (2018) 582. 
  2. H. Zhu, R. He, J. Mao, Q. Zhu, C. Li, J. Sun, W. Ren, Y. Wang, Z. Liu, Z. Tang, A. Sotnikov, Z. Wang, D. Broido, D. J. Singh, G. Chen, K. Nielsch, Z. F. Ren. Discovery of ZrCoBi-based half-Heuslers with high thermoelectric conversion efficiency. Nature Communications 9 (2018) 2497. 
  3. H. Zhou, F. Yu, J. Sun, R. He, S. Chena, C.-W. Chua, Z. F. Ren. Highly active catalyst derived from a 3D foam of Fe(PO3)2/Ni2P for extremely efficient water oxidation. Proc. Natl. Acad. Sci. USA 114 (2017) 5607. 
  4. J. Shuai, J. Mao, S. Song, Q. Zhu, J. Sun, Y. Wang, R. He, J. Zhou, G. Chen, D. J. Singh, Z. F. Ren. Tuning the carrier scattering mechanism to effectively improve the thermoelectric properties. Energy Environ. Sci. 10 (2017) 799. 
  5. R. He, D. Kraemer, J. Mao, Q. Jie, Y. Lan, C.a Li, J. Shuai, H. S. Kim, D. Broido, G. Chen, Z. F. Ren. Achieving high power factor and output power density in p-type half-Heuslers Nb1-xTixFeSb. Proc. Natl. Acad. Sci. USA 113 (2016) 13576. 
  6. D. Luo, F. Wang, J. Zhu, F. Cao, Y. Liu, X. Li, R. C. Willson, Z. Yang, C.-W. Chu, Z. F. Ren. Nanofluid of graphene-based amphiphilic Janus nanosheets for tertiary or enhanced oil recovery: High performance at low concentration. Proc. Natl. Acad. Sci. USA 113 (2016) 7711. 
  7. H. S. Kim, W. Liu, G. Chen, C.-W. Chu, Z. F. Ren. Relationship between Thermoelectric Figure of Merit and Energy Conversion Efficiency. Proc. Natl. Acad. Sci. USA 112 (2015) 8205. 
  8. B. Poudel, Q. Hao, Y. Ma, Y. Lan, A. Minnich, B. Yu, X. Yan, D. Wang, A. Muto, D. Vashaee, X. Chen, J. Liu, M. S. Dresselhaus, G. Chen, Z. F. Ren. High-Thermoelectric Performance of Nanostructured Bismuth Antimony Telluride Bulk Alloys. Science 320 (2008) 634. 
  9. Z. F. Ren, Z. P. Huang, J. W. Xu, J. H. Wang, P. Bush, M. P. Siegal, and P. N. Provencio. Synthesis of Large Arrays of Well-Aligned Carbon Nanotubes on Glass. Science 282 (1998) 1105. 
  10. C. C. Tsuei, J. R. Kirtley, M. Rupp. J. Z. Sun, A. Gupta, M. B. Ketchen, C. A. Wang, Z. F. Ren, J. H. Wang, M. Bhushan. Half-Integer Flux Quantum Effect and Pairing Symmetry in High-Tc One-Layer Tetragonal Tl2Ba2CuO6+? Superconductors. Science 271 (1996) 329. 
  11. C. C. Tsuei, J. R. Kirtley, Z. F. Ren, J. H. Wang, H. Raffy, and Z. Z. Li. Pure ????2–??2 order-parameter symmetry in the tetragonal superconductor TI2Ba2CuO6+δ. Nature 387 (1997) 481. 
  12. A. A. Tsvetkov, D. van der Marel, K. A. Moler, J. R. Kirtley, J. L. de Boer, A. Meetsma, Z. F. Ren, N. Koleshnikov, D. Dulic, A. Damascelli, M. Grüninger, J. Schützmann, J. W. van der Eb, H. S. Somal, and J. H. Wang. Global and local measures of the intrinsic Josephson coupling in Tl2Ba2CuO6 as a test of the interlayer tunnelling model. Nature 395 (1998) 360.