About

J. Tyler Mefford is an Assistant Professor in the Department of Chemical Engineering at the University of California, Santa Barbara. His research focuses on the intersection of engineering, chemistry, and materials to understand and control electron and ion transfer at electrified interfaces. His group develops novel redox-active polymers and inorganic electrode materials aimed at applications in electrochemical energy conversion, storage, and chemical separations. His work emphasizes understanding the non-equilibrium properties of electrochemical systems and reaction mechanisms across various time and length scales, utilizing device development, operando spectroscopy, microscopy, scattering techniques, and computational methods. Dr. Mefford holds a BS in Chemistry from Stanford University (2012) and a PhD in Chemistry from The University of Texas at Austin (2016). His contributions to the field have been recognized through awards such as the 2020 Best In-situ and Operando Characterization Presentation Award at MRS, the 2016 Excellence in Renewable & Clean Energy Research Award from UT Energy Institute, and the 2016 Nano Portfolio Presentation Award from the University of Texas at Austin. His research aims to advance sustainable energy technologies by understanding and manipulating electrochemical processes at the molecular and device levels.

Research topics

• Materials science
• Nanotechnology
• Chemistry
• Physical chemistry
• Chemical physics
• Medicine
• Combinatorial chemistry
• Chemical engineering
• Metallurgy
• Pathology
• Computational chemistry

Selected publications

• pH Controls Charge Localization in Redox-Active Ladder Polymers

  Journal of the American Chemical Society · 2026-02-25

  articleSenior authorCorresponding

  Organic mixed ionic-electronic conducting polymers (OMIECs) are versatile active materials for applications in transistors, energy storage, and bioelectronics. To meet the varied demands of these technologies, the chemical structure of an OMIEC is often designed with the goal of modifying the localization of added charge, modulating the energetics of frontier orbitals, and altering the degree of charge transfer to charge compensating species. Here, we show that the redox behavior of the archetypal ladder OMIEC, poly(benzimidazobenzophenanthroline) (BBL), is fundamentally modulated by the pH of the electrolyte, even under neutral to basic conditions where protons were previously assumed to not participate in redox processes. Through a combination of electrochemical characterization, operando Raman spectroscopy, ab initio simulations and electrochemical modeling with a multicomponent regular solution framework, we untangle BBL's redox mechanism. Our results reveal the competitive formation of proton-coupled and salt cation-coupled redox states, each possessing distinct characteristics. Notably, we find that proton-coupled redox dominates at neutral pHs, challenging the prevailing view that BBL is reduced to its salt-compensated bipolaronic form in this pH regime. Using a modified Pourbaix diagram, we illustrate how the balance between a proton-coupled and salt cation-coupled form of BBL can be continuously tuned via pH and applied potential. These findings highlight the complexity of multiphase coexistence and nontrivial effect of pH in controlling the redox properties of n-type ladder OMIECs, paving the way to understand and ultimately control a wide range of aqueous electrochemical reactions.

  PublisherDOI

• A New Bronze Age? Evaluation of Cu-Sn Intermetallic Substrates in Tin Anodes for Alkaline Aqueous Batteries

  ECS Meeting Abstracts · 2025-07-11

  article

  Tin is an exciting emerging metal anode for high energy density aqueous batteries due to the four-electron Sn(OH) 6 2- /Sn redox couple in alkaline electrolyte (903 mAh g -1 or 6,560 Ah L -1 ) with high reversibility, limited hydrogen evolution, and dendrite-free plating. The alkaline Sn system has a kinetically asymmetric redox pathway, with charge consisting of a direct four-electron plating and discharge progressing in a stepwise 2+2 electron stripping through a Sn(OH) 3 - intermediate. Due to the nature of an electrochemical deposition reaction, an anode-free Sn battery requires a substrate upon which Sn nuclei can form and grow during plating. This substrate’s available surface area, wettability, affinity with Sn, and catalytic properties affect the kinetics of the reaction in both the charge and discharge directions. In this work, we evaluate the behavior of alkaline Sn anodes with carbon fiber and copper substrates to determine the substrate effect on plating morphology, coulombic and voltaic efficiencies, and catalytic capabilities. The strong interaction between Cu and Sn promotes the formation of a Cu 6 Sn 5 alloy interphase during deposition and supports the formation of a Sn(OH) x surface intermediate during oxidation, allowing more efficient nucleation during charging and lower discharge overpotential, in particular for the Sn(OH) 3 - / Sn(OH) 6 2- redox, resulting in enhanced voltage efficiency and improved rate performance. This research emphasizes the pivotal role of substrate design in advancing the efficiency of multi-electron aqueous battery electrodes.

  PublisherDOI

• pH-dependent Scaling Relations and Ion Insertion Promote Bifunctional Oxygen Electrocatalysis on MnO2

  ChemRxiv · 2025-10-14

  preprintSenior author

  Designing electrocatalysts that efficiently mediate both the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) remains a central challenge in electrochemical energy conversion and storage. Most catalysts exhibit activity for one reaction at the expense of the other due to adsorbate scaling relations. Here, we report that 𝛼-KxMnO2 defies this trade-off, exhibiting simultaneous improvements for both OER and ORR with increasing electrolyte pH. Using rotating ring disk electrochemistry (RRDE), high-resolution transmission electron microscopy (HRTEM), and operando X-ray and infrared spectromicroscopies, we rule out morphological changes and site blocking as causes of this unusual pH effect. Instead, grand-canonical DFT shows that a pH-dependent interfacial electric field strengthens the adsorption of key intermediates at high pH, leading to non-Nernstian shifts towards lower overpotentials. Simultaneously, electrochemical K+ (de)insertion promotes high bifunctional activity by stabilizing Mn3+ sites for ORR and Mn4+ sites for OER. These mechanistic findings establish a generalizable strategy for breaking conventional catalytic trade-offs by coupling electrolyte engineering and ion insertion to enhance electrocatalytic performance.

  PublisherDOI

• Role of Ionization Energy on Mixed Conduction in Polythiophene-Derived Polyelectrolyte Complexes

  ACS Macro Letters · 2025-06-16 · 2 citations

  article

  Conjugated polyelectrolyte complexes formed by the electrostatic compatibilization between a conjugated and an insulating polyelectrolyte are a versatile design platform for highly processable, high performing polymeric mixed ion–electron conductors. While electrostatic mediation in complexes allows for structure and property control, a fundamental understanding of how the properties of the constituent conjugated polyelectrolyte (CPE) translate to the resulting complex performance is necessary for future designs. To investigate the role of CPE architecture on the overall charge transport properties of the resulting complex properties, here we compare a water-soluble cationic poly(alkoxythiophene) derivative based on poly(3-alkoxy-4-methylthiophene) with an imidazolium pendant unit and bromide counterion to an analogous complex with poly(sodium 4-styrenesulfonate). Through spectroscopic, morphological, electrochemical, and charge transport characterization, we find that poly(alkoxythiophene)-based complexes exhibit high mixed conductivity, enhanced electrochemical stability, improved doping efficiency, and lower oxidation potential, relative to previously reported poly(3-alkylthiophene)-based complexes, making them more suitable candidates for electrochemical applications. Importantly, both CPE and complex films based on the poly(3-alkoxy-4-methylthiophene) chemistry display electronic conductivities on the order of 10–2–10–3 S/cm and impressive ionic conductivities up to the order of 10–4 S/cm, despite the ordered morphology of the 3-alkoxy-4-methylthiophene backbone. We make a key observation that the enhancement of the electronic conductivity of the CPE from an alkyl to alkoxythiophene backbone does not necessarily improve the electronic conduction of the resulting complex as observed in previous reports, thereby underscoring the role of complexation thermodynamics, dielectric strength of the electrostatic complex, and complex morphology on mixed conduction. This study provides fundamental insights governing future design rules of mixed-conducting polyelectrolyte complexes for next-generation energy applications.

  PublisherDOI

• pH controls charge localization in redox-active ladder polymers

  ChemRxiv · 2025-06-09 · 1 citations

  preprintOpen accessSenior author

  Organic mixed ionic-electronic conducting polymers (OMIECs) are versatile active materials for applications in transistors, energy storage, and bioelectronics. To meet the varied demands of these technologies, the chemical structure of an OMIEC is often designed with the goal of modifying the localization of added charge, modulating the energetics of frontier orbitals, and altering the degree of charge transfer to charge compensating species. Here, we show that the redox behavior of the archetypal ladder OMIEC, poly(benzimidazobenzophenanthroline) (BBL), is fundamentally modulated by the pH of the electrolyte, even under neutral to basic conditions where protons were previously assumed to not participate in redox processes. Through a combination of electrochemical characterization, operando Raman spectroscopy, ab initio simulations and electrochemical modeling with a multi-component regular solution framework, we untangle BBL’s redox mechanism. Our results reveal the competitive formation of proton-coupled and salt cation-coupled redox states, each possessing distinct characteristics. Notably, we find that proton-coupled redox dominates at neutral pHs, challenging the prevailing view that BBL is reduced to its salt-compensated bipolaronic form in this pH regime. Using a modified Pourbaix diagram, we illustrate how the balance between a proton-coupled and salt cation-coupled BBL form of BBL can be continuously tuned via pH and applied potential. These findings highlight the complexity of multi-phase coexistence and non-trivial effect of pH in controlling the redox properties of OMIECs, paving the way to understand and ultimately control a wide range of aqueous electrochemical reactions.

  PublisherOA PDFDOI

• A Reversible Four-electron Sn Metal Aqueous Battery

  ChemRxiv · 2024-01-22 · 1 citations

  preprintOpen accessSenior author

  Sn is a promising metal anode for aqueous batteries due to its dendrite-free plating, large hydrogen evolution overpotential, and high theoretical capacity with up to four-electron redox per Sn atom. However, practically achieving the theoretical capacity for Sn remains challenging, with only limited cell energy densities demonstrated thus far. We validate a kinetically asymmetric [Sn(OH)6]2-/Sn redox pathway involving a direct four-electron plating and a stepwise 2+2 electron stripping through a [Sn(OH)3]- intermediate, which decreases the Coulombic efficiency (CE) by shuttling to the cathode and promoting chemical self-discharge. By using ion-selective membranes to suppress [Sn(OH)3]- crossover, we demonstrate Sn-Ni full cells with high round-trip efficiency (~80%) and energy density (143.1 Wh L-1). The results provide key understandings to the tradeoffs in engineering reversible multi-electron metal anodes and define a new benchmark for practical energy density that exceeds Sn-based aqueous batteries to date.

  PublisherOA PDFDOI

• In-Situ Liquid-Electrochemical X-Ray and Electron Microscopy for Multi-Modal Energy Materials Characterization

  ECS Meeting Abstracts · 2024-08-09

  article

  In-situ liquid cell electron and x-ray microscopy have enabled dynamic studies of electrochemical reactions in energy materials and revealed relationships between the performance, structure, and chemical composition of these material systems. Such fundamental relationships are critical to improving the performance of batteries, catalysts, and other energy materials. Growing research interest in energy materials systems has accelerated the development of in-situ liquid-electrochemical microscopy techniques into mature and robust characterization workflows using novel and versatile scientific hardware. Multiple characterization techniques or in-situ processing steps are often required to fully understand the mechanisms governing the behavior of energy materials for all relevant length scales and environmental conditions. A multi-modal workflow combining in-situ liquid-electrochemical transmission electron, X-ray synchrotron and scanning electron microscopy methods is presented. The breadth of research applications is discussed, including the study of chemical dynamics and structural changes to micron-scale Li x FePO 4 battery particles during lithium-ion insertion/extraction, electrocatalytic behavior of β-Co(OH) 2 platelet particles, and electrochemical oxidation of copper nanoparticles under reductive electrolytic conditions. New insights into these materials systems provided by these experiments will directly inform the development of predictive models for material performance and guide improvement of material design and synthesis. New scientific hardware and method development has been critical to in-situ nano-scale liquid cell microscopy and spectroscopy of electrochemical systems. Therefore, best-practice hardware and method design and development for these in-situ liquid-electrochemical microscopy experiments are also discussed. The connections between potentiostat, holder, and on-chip leads must be carefully considered with respect to different ground potentials, and the incorporation of real bulk-scale reference electrodes in this hardware has yielded quantitatively higher fidelity data with less degradation from further electrochemical cycling. Heating the sample or illuminating with light during in-situ electrochemical data collection has begun to further expand the range of environmental conditions that can be incorporated into experiments.

  PublisherDOI

• Effects of Electrolyte Composition on the Electrochemistry of Organic Mixed Conducting Polymer Electrodes

  ECS Meeting Abstracts · 2024-11-22

  articleSenior author

  Organic mixed ionic-electronic conductors (OMIECs) are semiconducting conjugated polymers that can transport both electrons and ions throughout their bulk. This property is enabled by electrochemical ion-insertion redox reactions that co-dope the polymer with mobile ions and electrons (or holes). These redox and mixed conduction capabilities provide functionality for applications including organic batteries, actuators, and organic electrochemical transistors. These various applications are enabled by a few fundamental OMIEC redox processes that involve polymer-electrolyte and polymer-electrode interfaces as well as mobile ions and significant amounts of incorporated solvent. Understanding the role of electrolyte in changing these redox processes can enable improved performance across a variety of devices. This work sets out to identify the role of electrolyte composition in changing the electrochemistry of a conjugated ladder polymer through a multi-faceted experimental and theoretical approach. We primarily focus our efforts on BBL, more formally called poly(benzimidazobenzophenanthroline). Using rotating disk electrochemistry, we find that electrolyte can cause a significant change in the voltage windows in which BBL is redox-active. Using operando UV-Vis and Raman spectroscopy measurements, we identify changes in BBL electrochemistry when operated in different electrolytes. To gain further insights about the redox mechanisms for this polymer, we use DFT to model our operando Raman data and principal component analysis to propose a charging mechanism that accounts for this electrolyte-dependent performance. Our results suggest that the accessible redox states of this polymer can dramatically change based on a modification of its local environment.

  PublisherDOI

• Development of High-Utilization Four-Electron Tin Anodes for Aqueous Batteries

  ECS Meeting Abstracts · 2024-11-22

  articleSenior author

  Developing high-energy density aqueous batteries is a vital step towards inexpensive and safe energy storage. A major challenge in this approach is achieving high utilization and reversibility with multi-electron metal anodes while operating near the water stability window. Of the main metal anode candidates (Zn, Al, Mg, Fe, Sn, etc.), Sn has recently received increasing attention due to its limited hydrogen evolution activity, dendrite-free plating, and high theoretical capacity for the four-electron Sn(OH) 6 2- /Sn redox couple in alkaline electrolytes (903 mAh g Sn -1 or 6,560 Ah L Sn -1 ). Understanding the reversibility of charge transfer processes that occur in aqueous batteries with metal anodes necessitates probing the solid, liquid, and gaseous phases that evolve during cycling. In this talk, we will discuss a robust toolbox of direct characterization tools developed to elucidate the electrochemical behavior of alkaline Sn batteries. Our work uncovers the origins of the kinetically asymmetric redox behavior, with direct four-electron plating during charging and discharge progressing in a stepwise 2+2 electron stripping through a Sn(OH) 3 - intermediate. The prolonged presence of the Sn(OH) 3 - intermediate presents both challenges and opportunities with the alkaline Sn system. On the one hand, if crossover cannot be prevented, Sn(OH) 3 - chemically reducing the cathode directly impacts coulombic efficiency. However, disproportionation of Sn(OH) 3 - can be driven near the anode, improving voltage efficiency. Through understanding and controlling these effects, we engineer a four-electron Sn alkaline battery with high energy-efficiency, high utilization, and long cycle-life.

  PublisherDOI

• A reversible four-electron Sn metal aqueous battery

  Joule · 2024-09-27 · 13 citations

  articleOpen accessSenior author
  PublisherOA PDFDOI

Frequent coauthors

• William C. Chueh

  35 shared

• Christoph Baeumer

  University of Twente

  34 shared

• William C. Chueh

  SLAC National Accelerator Laboratory

  34 shared

• Andrew R. Akbashev

  Paul Scherrer Institute

  32 shared

• Keith J. Stevenson

  Lomonosov Moscow State University

  16 shared

• Keith P. Johnston

  The University of Texas at Austin

  13 shared

• Michal Bajdich

  13 shared

• William G. Hardin

  The University of Texas at Austin

  12 shared

Labs

• J. Tyler MeffordPI

Awards & honors

• 2020 Best In-situ and Operando Characterization Presentation…
• 2016 Excellence in Renewable & Clean Energy Research Award,…
• 2016 Nano Portfolio Presentation Award, University of Texas…