Growth characteristics and the mass transfer mechanism of single bubble on a photoelectrode at different electrolyte concentrations.

In the photoelectrochemical water splitting reaction, the bubble attached to the working electrode is an essential factor affecting the reaction resistance, current density and gas-liquid mass transfer. An experimental measurement system based on an electrochemical workstation synchronously coupled with a high-speed microscopic camera was proposed and used to systematically study the growth kinetics and mass transfer mechanism of single oxygen bubbles at different electrolyte concentrations (Na2SO4, 0.1-2.0 M) on the TiO2 photoanode surface. Under constant voltage and constant current control conditions, when the electrolyte concentration increases, the bubble detachment diameter and the bubble detachment frequency gradually decrease. The bubble coverage equation expressed in terms of gas evolution efficiency is proposed and is associated with the photocurrent and bubble radius. The average bubble coverage and average gas evolution efficiency decrease when the electrolyte concentration is increased. According to the Sherwood dimensionless number, various mass transfer coefficients during bubble growth were calculated. The results show that the average total mass transfer coefficient is positively correlated with the change trend of the electrolyte concentration, and the mass transfer coefficient of single-phase natural convection is one order of magnitude larger than the mass transfer coefficient of bubble-induced convection. Finally, a conclusion on the transient mass transfer process in the bubble evolution process was obtained, that is, the mass transfer coefficient of single-phase natural convection and the total mass transfer coefficient remain high during the first growth stage, and gradually decrease during the second growth stage. Therefore, regulating the electrolyte concentration can effectively promote the gas-liquid mass transfer in the photoelectrochemical water splitting reaction.

Influence of subatmospheric pressure on bubble evolution on the TiO2 photoelectrode surface.

The increase of reaction resistance caused by bubble nucleation and long-time growth on the surface of the photoelectrode is an important factor that leads to the low efficiency of photoelectrochemical water splitting. In this study, we adopted an electrochemical workstation synchronous with a high-speed microscopic camera system to achieve in situ observation of oxygen bubble behavior on the surface of TiO2 and to study the internal relationship between the geometric parameters of oxygen bubbles and photocurrent fluctuations under different pressures and laser powers. The results indicate that with the decrease of pressure, the photocurrent decreases gradually and the bubble departure diameter increases gradually. In addition, the nucleation waiting stage and the growth stage of bubbles are both shortened. However, the difference between the average photocurrents corresponding to the moment of bubble nucleation and the stable growth stage hardly changes with the pressure. The production rate of gas mass reaches a peak near 80 kPa. In addition, a force balance model suitable for different pressures is constructed. It is found that as the pressure decreases from 97 kPa to 40 kPa, the proportion of the thermal Marangoni force in the Marangoni force decreases from 29.4% to 21.3%, while the proportion of the concentration Marangoni force increases from 70.6% to 78.7%, indicating that the concentration Marangoni force is the main factor affecting the bubble departure diameter under subatmospheric pressure conditions.

Human endoderm stem cells reverse inflammation-related acute liver failure through cystatin SN-mediated inhibition of interferon signaling.

Acute liver failure (ALF) is a life-threatening disease that occurs secondary to drug toxicity, infection or a devastating immune response. Orthotopic liver transplantation is an effective treatment but limited by the shortage of donor organs, the requirement for life-long immune suppression and surgical challenges. Stem cell transplantation is a promising alternative therapy for fulminant liver failure owing to the immunomodulatory abilities of stem cells. Here, we report that when transplanted into the liver, human endoderm stem cells (hEnSCs) that are germ layer-specific and nontumorigenic cells derived from pluripotent stem cells are able to effectively ameliorate hepatic injury in multiple rodent and swine drug-induced ALF models. We demonstrate that hEnSCs tune the local immune microenvironment by skewing macrophages/Kupffer cells towards an anti-inflammatory state and by reducing the infiltrating monocytes/macrophages and inflammatory T helper cells. Single-cell transcriptomic analyses of infiltrating and resident monocytes/macrophages isolated from animal livers revealed dramatic changes, including changes in gene expression that correlated with the change of activation states, and dynamic population heterogeneity among these cells after hEnSC transplantation. We further demonstrate that hEnSCs modulate the activation state of macrophages/Kupffer cells via cystatin SN (CST1)-mediated inhibition of interferon signaling and therefore highlight CST1 as a candidate therapeutic agent for diseases that involve over-activation of interferons. We propose that hEnSC transplantation represents a novel and powerful cell therapeutic treatment for ALF.