Semiconductor Heterostructure (SrFe0.3TiO3-ZnO) Electrolyte with High Proton Conductivity for Low-Temperature Ceramic Electrochemical Cells.

In recent years, ceramic cells based on high proton conductivity have attracted much attention and can be employed for hydrogen production and electricity generation, especially at low temperatures. Nevertheless, attaining a high power output and durability is challenging, especially at low operational temperatures. In this regard, we design semiconductor heterostructure SFT-ZnO (SrFe0.3TiO3-ZnO) materials to function as an electrolyte for fuel cell and electrolysis applications. Using this approach, the functional semiconductor heterostructure can deliver a better power output and high ionic and proton conductivity at low operational temperatures. The prepared cell in fuel cell mode has demonstrated excellent performance of 700 mW cm-2 and proton performance of 540 mW cm-2 at the low temperature of 520 °C, suggesting dominant proton conduction. Further, the prepared cell delivers exceptional current densities of 1.18 and 0.38 A cm-2 (at 1.6 and 1.3 V, respectively) at 520 °C in the electrolysis mode. Our electrochemical cell is stable in fuel and electrolysis mode at a low temperature of 500 °C.

Exceptionally high proton conductivity in Eu2O3 by proton-coupled electron transfer mechanism.

Proton conductors are typically developed by doping to introduce structural defects such as oxygen vacancies to facilitate ionic transport through structural bulk conduction mechanism. In this study, we present a novel electrochemical proton injection method via an in situ fuel cell process, demonstrating proton conduction in europium oxide (Eu2O3) through a surficial conduction mechanism for the first time. By tuning Eu2O3 into a protonated form, H-Eu2O3, we achieved an exceptionally high proton conductivity of 0.16 S cm-1. Distribution of relaxation time (DRT) analysis was employed to investigate the proton transport behavior and reveal the significant contribution of surface proton transport to the overall conductivity of Eu2O3. Remarkably, H-Eu2O3 exhibited a low activation energy for ionic transport, comparable to the best ceramic electrolytes available. The proton-coupled electron transfer (PCET) mechanism describes this novel surficial proton conduction mechanism. These findings provide new possibilities for developing advanced proton conductors with improved performance.

Optimizing oxygen vacancies and electrochemical performance of CeO2-δ nanosheets through the combination of di- and tri-valent doping.

Ceramic fuel cells presently hold an important position in the future of sustainable energy. However, new concepts and designs are vital for each individual cell's component materials to improve the overall power output and stability. The limited ionic conductivity of the electrolyte component is one major challenge among these. In the present work, we developed nanosheets with a cubic fluoride structure of CeO2 and introduced the di- and tri-valent doping of La and Sr to study their impact on oxygen vacancies and its ionic transport, keeping in mind the fact that CeO2 is reduced when exposed to a reducing atmosphere. The attained La- and Sr-doped fluorite structures of CeO2 exhibited good ionic conductivity of >0.05 S cm-1 at low temperature, and their use in a fuel cell resulted in achieving a power output of >900 mW cm-2 while operating at 550 °C. Therefore, we have found that laterally combining di- and tri-valent doping could be textured to give a highly oxygen-deficient CeO2 structure with high ionic transport. Furthermore, various microscopic and spectroscopic analyses, such as HR-TEM, XPS, Raman, UV-visible, EIS, and density functional theory, were applied to investigate the change in structural properties and mechanism of the ionic transport of the synthesized La and Sr co-doped CeO2 electrolyte. This work provides some new insights for designing high-ionic-conductivity electrolytes from low-cost semiconductor oxides for energy storage and conversion devices.

2D MXenes Embedded Perovskite Hydrogels for Efficient and Stable Solar Evaporation.

Solar evaporation is a facile and promising technology to efficiently utilize renewable energy for freshwater production and seawater desalination. Here, the fabrication of self-regenerating hydrogel composed of 2D-MXenes nanosheets embedded in perovskite La 0.6Sr 0.4Co 0.2Fe 0.8O3- δ (LSCF)/polyvinyl alcohol hydrogels for efficient solar-driven evaporation and seawater desalination is reported. The mixed dimensional LSCF/Ti3C2 composite features a localized surface plasmonic resonance effect in the polymeric network of polyvinyl alcohol endows excellent evaporation rates (1.98 kg m-2 h-1) under 1 k Wm-2 or one sun solar irradiation ascribed by hydrophilicity and broadband solar absorption (96%). Furthermore, the long-term performance reveals smooth mass change (13.33 kg m-2) during 8 h under one sun. The composite hydrogel prompts the dilution of concentrated brines and redissolves it back to water (1.2 g NaCl/270 min) without impeding the evaporation rate without any salt-accumulation. The present research offers a substantial opportunity for solar-driven evaporation without any salt accumulation in real-life applications.

Toward next-generation fuel cell materials.

The fuel cell's three layers-anode/electrolyte/cathode-convert fuel's chemical energy into electricity. Electrolyte membranes determine fuel cell types. Solid-state and ceramic electrolyte SOFC/PCFC and polymer based PEMFC fuel cells dominate fuel cell research. We present a new fuel cell concept using next-generation ceramic nanocomposites made of semiconductor-ionic material combinations. A built-in electric field driving mechanism boosts ionic (O2- or H+ or both) conductivity in these materials. In a fuel cell device, non-doped ceria or its heterostructure might attain 1 Wcm-2 power density. We reviewed promising functional nanocomposites for that range. Ceria-based and multifunctional semiconductor-ionic electrolytes will be highlighted. Owing to their simplicity and abundant resources, these materials might be used to make fuel cells cheaper and more accessible.

High-performing and stable semiconductor yttrium-doped gadolinium electrolyte for low-temperature solid oxide fuel cells.

High-performing electrolytes at low operating temperatures have become an inevitable trend in the development of low-temperature solid oxide fuel cells (LT-SOFCs). Such electrolytes have drawn significant attention due to their appeal for high performance. Herein, we propose a new material by doping Y3+ into Gd2O3 for LT-SOFC electrolyte use. The prepared material was characterized in terms of crystal structure, surface, and interface properties, followed by its application in LT-SOFCs. YDG delivered promising SOFC performance with a power density of 1046 mW cm-2 at 550 °C along with high ionic conductivity of 0.19 S cm-1. Moreover, impedance spectra revealed that YDG exhibited the least ohmic resistance of 0.06-0.09 Ω cm2 at 550-460 °C. Furthermore, stable operation for 60 h demonstrated the chemical stability of the material in reduced temperature environments. Density function theory was also applied to analyze the electronic band structure and density of states of the synthesized sample. Our findings thus certify that YDG as a high-performing electrolyte at low operating temperatures.

Modulating the Energy Band Structure of the Mg-Doped Sr0.5Pr0.5Fe0.2Mg0.2Ti0.6O3-δ Electrolyte with Boosted Ionic Conductivity and Electrochemical Performance for Solid Oxide Fuel Cells.

Achieving fast ionic conductivity in the electrolyte at low operating temperatures while maintaining the stable and high electrochemical performance of solid oxide fuel cells (SOFCs) is challenging. Herein, we propose a new type of electrolyte based on perovskite Sr0.5Pr0.5Fe0.4Ti0.6O3-δ for low-temperature SOFCs. The ionic conducting behavior of the electrolyte is modulated using Mg doping, and three different Sr0.5Pr0.5Fe0.4-xMgxTi0.6O3-δ (x = 0, 0.1, and 0.2) samples are prepared. The synthesized Sr0.5Pr0.5Fe0.2Mg0.2Ti0.6O3-δ (SPFMg0.2T) proved to be an optimal electrolyte material, exhibiting a high ionic conductivity of 0.133 S cm-1 along with an attractive fuel cell performance of 0.83 W cm-2 at 520 °C. We proved that a proper amount of Mg doping (20%) contributes to the creation of an adequate number of oxygen vacancies, which facilitates the fast transport of the oxide ions. Considering its rapid oxide ion transport, the prepared SPFMg0.2T presented heterostructure characteristics in the form of an insulating core and superionic conduction via surface layers. In addition, the effect of Mg doping is intensively investigated to tune the band structure for the transport of charged species. Meanwhile, the concept of energy band alignment is employed to interpret the working principle of the proposed electrolyte. Moreover, the density functional theory is utilized to determine the perovskite structures of SrTiO3-δ and Sr0.5Pr0.5Fe0.4-xMgxTi0.6O3-δ (x = 0, 0.1, and 0.2) and their electronic states. Further, the SPFMg0.2T with 20% Mg doping exhibited low dissociation energy, which ensures the fast and high ionic conduction in the electrolyte. Inclusively, Sr0.5Pr0.5Fe0.4Ti0.6O3-δ is a promising electrolyte for SOFCs, and its performance can be efficiently boosted via Mg doping to modulate the energy band structure.

Development of a Core-Shell Heterojunction TiO2 /SrTiO3 Electrolyte with Improved Ionic Conductivity.

The front cover artwork is provided by Prof. Faze Wang's group at the Southeast University. The built-in electric field created by the semiconductor heterostructure confines the proton transport on the surface layer of the nanocomposite core-shell heterostructure imparting faster ion transport and lower activation energy. Read the full text of the Research Article at 10.1002/cphc.202200170.

Development of a Core-Shell Heterojunction TiO2 /SrTiO3 Electrolyte with Improved Ionic Conductivity.

Lately, semiconductor-membrane fuel cells (SMFCs) have attained significant interest and great attention due to the deliverance of high performance at low operational temperatures, <550 °C. This work has synthesized the nanocomposite core-shell heterostructure (TiO2 -SrTiO3 ) electrolyte powder by employing the simple hydrothermal method for the SMFC. The SrTiO3 was grown in situ on the surface of TiO2 to form a core-shell structure. A heterojunction mechanism based on the energy band structure is proposed to explain the ion transport pathway and promoted protonic conductivity. The core-shell heterostructure (TiO2 -SrTiO3 ) was utilized as an electrolyte to reach the peak power density of 951 mW cm-2 with an open-circuit voltage of 1.075 V at 550 °C. The formation of core-shell heterostructure among TiO2 and SrTiO3 causes redistribution of charges and establishes a depletion region at the interface, which confined the protons' transport on the surface layer with accelerated ion transport and lower activation energy. The current work reveals novel insights to understand enhanced proton transport and unique methodology to develop low-temperature ceramic fuel cells with high performance.