Zi Wei

Synthesis and characterization of conductive, biodegradable, elastomeric polyurethanes for biomedical applications

Biodegradable conductive polymers are currently of significant interest in tissue repair and regeneration, drug delivery, and bioelectronics. However, biodegradable materials exhibiting both conductive and elastic properties have rarely been reported to date. To that end, an electrically conductive polyurethane (CPU) was synthesized from polycaprolactone diol, hexadiisocyanate, and aniline trimer and subsequently doped with (1S)-(+)-10-camphorsulfonic acid (CSA). All CPU films showed good elasticity within a 30% strain range. The electrical conductivity of the CPU films, as enhanced with increasing amounts of CSA, ranged from 2.7 ± 0.9 × 10(-10) to 4.4 ± 0.6 × 10(-7) S/cm in a dry state and 4.2 ± 0.5 × 10(-8) to 7.3 ± 1.5 × 10(-5) S/cm in a wet state. The redox peaks of a CPU1.5 film (molar ratio CSA:aniline trimer = 1.5:1) in the cyclic voltammogram confirmed the desired good electroactivity. The doped CPU film exhibited good electrical stability (87% of initial conductivity after 150 hours charge) as measured in a cell culture medium. The degradation rates of CPU films increased with increasing CSA content in both phosphate-buffered solution (PBS) and lipase/PBS solutions. After 7 days of enzymatic degradation, the conductivity of all CSA-doped CPU films had decreased to that of the undoped CPU film. Mouse 3T3 fibroblasts proliferated and spread on all CPU films. This developed biodegradable CPU with good elasticity, electrical stability, and biocompatibility may find potential applications in tissue engineering, smart drug release, and electronics.

Ultra-long electron lifetime induced efficient solar energy storage by an all-vanadium photoelectrochemical storage cell using methanesulfonic acid

The properties of a supporting electrolyte are critically important to any photo- or electrochemical cells. In this study, we conducted studies on and characterized an all-vanadium photoelectrochemical storage cell (all-V PESC) for highly efficient solar energy storage using methanesulfonic acid (MSA) as a promising supporting electrolyte. Linear sweep voltammetry (LSV) and zero resistance ammetry (ZRA) studies of the all-V PESC show greatly improved photoelectrochemical properties of MSA over conventional H2SO4. To elucidate its heightened performance, the conductivity and reaction kinetics of the system were investigated using four-probe conductivity measurements and electrochemical impedance spectroscopy (EIS), respectively. The EIS results demonstrate vastly reduced charge transfer resistance and interfacial capacitance at the photoelectrode/electrolyte interface via ultra-long photoelectron lifetime; while the conductivity measurements reveal a comparable bulk ionic conductivity to H2SO4. Cell efficiency tests indicate a nearly 19-fold enhancement in incident photon-to-electron conversion efficiency (IPCE) and a high faradaic efficiency (84.8%) during a continuous 60 h operation using MSA as the supporting electrolyte. Besides, multiple cyclic voltammetry (CV) scans on the electrolyte along with XRD and SEM characterization of the photoelectrode corroborate the exceptional chemical stability of MSA.

An All-vanadium Continuous-flow Photoelectrochemical Cell for Extending State-of-charge in Solar Energy Storage

Greater levels of solar energy storage provide an effective solution to the inherent nature of intermittency, and can substantially improve reliability, availability, and quality of the renewable energy source. Here we demonstrated an all-vanadium (all-V) continuous-flow photoelectrochemical storage cell (PESC) to achieve efficient and high-capacity storage of solar energy, through improving both photocurrent and photocharging depth. It was discovered that forced convective flow of electrolytes greatly enhanced the photocurrent by 5 times comparing to that with stagnant electrolytes. Electrochemical impedance spectroscopy (EIS) study revealed a great reduction of charge transfer resistance with forced convective flow of electrolytes as a result of better mass transport at U-turns of the tortuous serpentine flow channel of the cell. Taking advantage of the improved photocurrent and diminished charge transfer resistance, the all-V continuous-flow PESC was capable of producing ~20% gain in state of charge (SOC) under AM1.5 illumination for ca. 1.7 hours without any external bias. This gain of SOC was surprisingly three times more than that with stagnant electrolytes during a 25-hour period of photocharge.

Development of dopant-free conductive bioelastomers.

Conductive biodegradable materials are of great interest for various biomedical applications, such as tissue repair and bioelectronics. They generally consist of multiple components, including biodegradable polymer/non-degradable conductive polymer/dopant, biodegradable conductive polymer/dopant or biodegradable polymer/non-degradable inorganic additives. The dopants or additives induce material instability that can be complex and possibly toxic. Material softness and elasticity are also highly expected for soft tissue repair and soft electronics. To address these concerns, we designed a unicomponent dopant-free conductive polyurethane elastomer (DCPU) by chemically linking biodegradable segments, conductive segments, and dopant molecules into one polymer chain. The DCPU films which had robust mechanical properties with high elasticity and conductivity can be degraded enzymatically and by hydrolysis. It exhibited great electrical stability in physiological environment with charge. Mouse 3T3 fibroblasts survived and proliferated on these films exhibiting good cytocompatibility. Polymer degradation products were non-toxic. DCPU could also be processed into a porous scaffold and in an in vivo subcutaneous implantation model, exhibited good tissue compatibility with extensive cell infiltration over 2 weeks. Such biodegradable DCPU with good flexibility and elasticity, processability, and electrical stability may find broad applications for tissue repair and soft/stretchable/wearable bioelectronics.

Length‐Scale‐Dependent Phase Transformation of LiFePO4: An In situ and Operando Study Using Micro‐Raman Spectroscopy and XRD

The charge and discharge of lithium ion batteries are often accompanied by electrochemically driven phase-transformation processes. In this work, two in situ and operando methods, that is, micro-Raman spectroscopy and X-ray diffraction (XRD), have been combined to study the phase-transformation process in LiFePO4 at two distinct length scales, namely, particle-level scale (∼1 μm) and macroscopic scale (∼several cm). In situ Raman studies revealed a discrete mode of phase transformation at the particle level. Besides, the preferred electrochemical transport network, particularly the carbon content, was found to govern the sequence of phase transformation among particles. In contrast, at the macroscopic level, studies conducted at four different discharge rates showed a continuous but delayed phase transformation. These findings uncovered the intricate phase transformation in LiFePO4 and potentially offer valuable insights into optimizing the length-scale-dependent properties of battery materials.

Improving the catalytic activity of Au/Pd core–shell nanoparticles with a tailored Pd structure for formic acid oxidation reaction

Unique morphology-tunable Au/Pd core–shell nanoparticles were synthesized by galvanic replacement of preformed Cu on hollow Au cores using different PdCl2 concentrations. The nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical analysis. The results showed that the structure of the nanocrystalline Pd on the hollow Au core surface was strongly dependent on the PdCl2 concentration. It was found that Pd2+ ions transport and react in the porous Cu layer, helping to create a continuous but porous structure which enlarges the Pd surface area and increases the electrochemical activity. In addition, the Au/Pd core–shell nanoparticles displayed superior electrochemical performance and stability in formic acid oxidation than commercial Pd black, especially for the ones synthesized using 2.5 mM PdCl2. The enhanced electrocatalytic performance may be attributed to the optimum electronic coupling effect caused by the interaction between the specific Pd structure and the hollow Au core.