About

Xiang Zhou is a Professor of Statistics and Data Science at Yale University. His research focuses on statistical methods and data science, contributing to the advancement of these fields through his academic work. As a faculty member, he supervises a team of postdoctoral researchers, PhD students, and visiting scholars, fostering a collaborative environment for research and education in statistics and data science.

Research topics

• Chemistry
• Organic chemistry
• Chemical engineering
• Nanotechnology
• Materials science
• Photochemistry
• Inorganic chemistry
• Chemical physics
• Thermodynamics
• Combinatorial chemistry

Selected publications

• Application of Polyelectrolyte Multilayer Coatings to Reduce Chloride Ion Crossover in an Asymmetric Seawater Electrolysis Cell

  ACS ES&T Engineering · 2025-09-16

  article

  Relatively inexpensive polyamide thin-film composite (TFC) membranes are being explored as separators in asymmetric seawater electrolysis cells for hydrogen gas production. However, the Cl– crossover from the saltwater catholyte to the anode must be minimized to prevent chlorine gas formation. We therefore examined whether coating the TFC active layer with negatively charged polyelectrolyte multilayers could reduce Cl– transport to the anode, using NO3– as a stable surrogate for Cl–. The coating reduced the crossover of NO3– by 19%, unlike in the pressure-driven reverse osmosis process where polyelectrolyte multilayer coatings on such TFC membranes have minimal effect on salt permeation. Using higher salt concentrations for both the inner and the last layers during the polyelectrolyte multilayer fabrication increased the negative charge of the multilayer and reduced the level of NO3– transport. Modeling of the electrolysis cell indicated that OH– was the dominant water ion in the polyelectrolyte multilayer (facing the alkaline catholyte). The concentrations of NO3– and OH– in the polyelectrolyte layer decreased with an increasing charge of the polyelectrolyte layer due to Donnan exclusion, resulting in a reduction of their migration and total fluxes. Overall, our findings demonstrated the feasibility of using polyelectrolyte multilayer coatings to control NO3– and thus Cl– ion transport during water electrolysis using a seawater catholyte.

  PublisherDOI

• Substantially Improved Microbial Electrosynthesis of Methane Achieved by Improving Hydrogen Retention and Flow Distribution through Porous Electrodes

  Environmental Science & Technology · 2025-07-01 · 6 citations

  article

  Efficient hydrogen utilization by microorganisms is crucial for improving the energy-to-chemical efficiency in microbial electrosynthesis (MES). We therefore developed a new rectangular zero-gap cell design featuring an extended flow path to improve hydrogen retention and conversion to biomethane. Multiphase flow modeling within porous carbon felt cathodes revealed the new configuration with a trapezoidal inlet substantially reduced flow dead zones and tripled hydrogen retention time versus circular cells. At −1 V vs Ag/AgCl, increasing catholyte flow rate from 0.8 to 2.5 mL/min raised current densities from 19 to 24 A/m2 (30 °C), reaching a peak Coulombic efficiency (CE) of 82% for methane production (7.0 L/L-d). Further increasing the flow rate to 7.5 mL/min or temperature to 37 °C slightly improved methane production (7.2–7.7 L/L-d) but reduced hydrogen retention in cells based on modeling results, lowering CEs and energy efficiencies due to unreacted hydrogen. Matching cathode potential to flow rates and temperatures could balance H2 production and retention, significantly improving CE to 96% toward 7.5 L/L-d methane production with a high energy efficiency of 36% (−0.95 V vs Ag/AgCl, 37 °C). These findings underscore the importance of improving flow distribution and hydrogen retention within zero-gap MES cells to enhance energy and Coulombic efficiencies.

  PublisherDOI

• Modeling Ion Transport across Thin-Film Composite Membranes During Saltwater Electrolysis

  Environmental Science & Technology · 2024-06-11 · 8 citations

  article

  Affordable thin-film composite (TFC) membranes are a potential alternative to more expensive ion exchange membranes in saltwater electrolyzers used for hydrogen gas production. We used a solution-friction transport model to study how the induced potential gradient controls ion transport across the polyamide (PA) active layer and support layers of TFC membranes during electrolysis. The set of parameters was simplified by assigning the same size-related partition and friction coefficients for all salt ions through the membrane active layer. The model was fit to experimental ion transport data from saltwater electrolysis with 600 mM electrolytes at a current density of 10 mA cm–2. When the electrolyte concentration and current density were increased, the transport of major charge carriers was successfully predicted by the model. Ion transport calculated using the model only minimally changed when the negative active layer charge density was varied from 0 to 600 mM, indicating active layer charge was not largely responsible for controlling ion crossover during electrolysis. Based on model simulations, a sharp pH gradient was predicted to occur within the supporting layer of the membrane. These results can help guide membrane design and operation conditions in water electrolyzers using TFC membranes.

  PublisherDOI

• Thin-Film Composite Membranes for Hydrogen Evolution with a Saline Catholyte Water Feed

  Environmental Science & Technology · 2024-01-03 · 5 citations

  articleOpen access

  Hydrogen gas evolution using an impure or saline water feed is a promising strategy to reduce overall energy consumption and investment costs for on-site, large-scale production using renewable energy sources. The chlorine evolution reaction is one of the biggest concerns in hydrogen evolution with impure water feeds. The “alkaline design criterion” in impure water electrolysis was examined here because water oxidation catalysts can exhibit a larger kinetic overpotential without interfering chlorine chemistry under alkaline conditions. Here, we demonstrated that relatively inexpensive thin-film composite (TFC) membranes, currently used for high-pressure reverse osmosis (RO) desalination applications, can have much higher rejection of Cl– (total crossover of 2.9 ± 0.9 mmol) than an anion-exchange membrane (AEM) (51.8 ± 2.3 mmol) with electrolytes of 0.5 M KOH for the anolyte and 0.5 M NaCl for the catholyte with a constant current (100 mA/cm2 for 20 h). The membrane resistances, which were similar for the TFC membrane and the AEM based on electrochemical impedance spectroscopy (EIS) and Ohm’s law methods, could be further reduced by increasing the electrolyte concentration or removal of the structural polyester supporting layer (TFC-no PET). TFC membranes could enable pressurized gas production, as this membrane was demonstrated to be mechanically stable with no change in permeate flux at 35 bar. These results show that TFC membranes provide a novel pathway for producing green hydrogen with a saline water feed at elevated pressures compared to systems using AEMs or porous diaphragms.

  PublisherOA PDFDOI

• Ceramic Thin-Film Composite Membranes with Tunable Subnanometer Poresfor Molecular Sieving By Atomic Layer Deposition

  ECS Meeting Abstracts · 2024-11-22

  article

  Membranes with tunable, sub-nanometer pores are needed for molecular separations in applications including water treatment, critical mineral extraction, and recycling. Ceramic membranes are a promising alternative to the polymeric membranes typically used in such applications due to their robust operation under harsh chemical conditions. However, current fabrication technologies fail to construct ceramic membranes suitable for selective molecular separations. In this presentation, we describe a ceramic thin film composite (TFC) membrane fabrication method that achieves sub-nm pore size control using atomic layer deposition (ALD) by incorporating a molecular-scale porogen. By co-dosing alkyl alcohols along with the H 2 O coreactant during Al 2 O 3 ALD, we incorporate alkoxide species in the film which create a continuous network of pores upon calcination. Varying the alkyl alcohol (methanol, ethanol, isopropanol) tunes the pore size. We use Fourier transform infrared absorption spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy to elucidate the surface chemistry and growth during the alcohol-modulated ALD as well as the subsequent pore formation. We evaluate the transport and separations properties of the ALD TFC membranes using a two-chamber diffusion cell with aqueous salt solutions. We measured a remarkable enhancement in the transport of Cl - compared to SO 4 2- (8.6 times faster) matching the selectivity of state-of-the-art polymer membranes. We attribute this selectivity to the dehydration of the large divalent ions within the subnanometer pores. In addition, permeation studies using neutral adsorbates revealed average pore sizes of ~7Å, 13Å, and 19Å for ALD TFC membranes prepared using methanol, ethanol, and isopropanol, respectively. This work provides the scientific basis for the design of ceramic membranes with subnanometer pores for molecular sieving using ALD.

  PublisherDOI

• Using a non-precious metal catalyst for long-term enhancement of methane production in a zero-gap microbial electrosynthesis cell

  Water Research · 2024-05-21 · 29 citations

  article
  PublisherDOI

• Data for Free-standing Membrane Incorporating Single-atom Catalysts for Ultrafast Electro-reduction of Low-concentration Nitrate

  Harvard Dataverse · 2023-02-14

  datasetOpen access

  Data for Free-standing Membrane Incorporating Single-atom Catalysts for Ultrafast Electro-reduction of Low-concentration Nitrate, PNAS

  PublisherDOI

• Electrochemical and hydraulic analysis of thin-film composite and cellulose triacetate membranes for seawater electrolysis applications

  Journal of Membrane Science · 2023-04-24 · 8 citations

  articleOpen access
  PublisherOA PDFDOI

• Electrochemical and Hydraulic Analysis of Thin-Film Composite and Cellulose Triacetate Membranes for Seawater Electrolysis Applications

  SSRN Electronic Journal · 2023-01-01

  articleOpen access
  PublisherDOI

• Relative Insignificance of Polyamide Layer Selectivity for Seawater Electrolysis Applications

  Environmental Science & Technology · 2023-09-18 · 19 citations

  article1st author

  Low-cost polyamide thin-film composite (TFC) membranes are being explored as alternatives to cation exchange membranes for seawater electrolysis. An optimal membrane should have a low electrical resistance to minimize applied potentials needed for water electrolysis and be able to block chloride ions present in a seawater catholyte from reaching the anode. The largest energy loss associated with a TFC membrane was the Nernstian overpotential of 0.74 V (equivalent to 37 Ω cm2 at 20 mA cm–2), derived from the pH difference between the anolyte and catholyte and not the membrane ohmic overpotential. Based on analysis using electrochemical impedance spectroscopy, the pristine TFC membrane contributed only 5.00 Ω cm2 to the ohmic resistance. Removing the polyester support layer reduced the resistance by 79% to only 1.04 Ω cm2, without altering the salt ion transport between the electrolytes. Enlarging the pore size (∼5 times) in the polyamide active layer minimally impacted counterion transport across the membrane during electrolysis, but it increased the total concentration of chloride transported by 60%. Overall, this study suggests that TFC membranes with thinner but mechanically strong supporting layers and size-selective active layers should reduce energy consumption and the potential for chlorine generation for seawater electrolyzers.

  PublisherDOI

Frequent coauthors

• Menachem Elimelech

  Yale University

  18 shared

• Jae‐Hong Kim

  Yale University

  17 shared

• Dahong Huang

  CAS Key Laboratory of Urban Pollutant Conversion

  11 shared

• Le Shi

  Pennsylvania State University

  9 shared

• Bruce E. Logan

  Pennsylvania State University

  7 shared

• Shuo Zhang

  7 shared

• Xuanhao Wu

  Zhejiang University

  6 shared

• Peng Liang

  Tsinghua University

  5 shared

Labs

• Xiang Zhou LabPI

  The Xiang Zhou Lab focuses on statistics and data science research.

Education

• Ph.D, Chemical and Environmental Engineering

  Yale University

• Bachelor, School of Environmental Engineering

  Tsinghua University

  2015