A novel yttrium stabilized zirconia and ceria composite electrolyte lowering solid oxide fuel cells working temperature to 400 °C.

Reducing the working temperature and improving the ionic conductivity of electrolytes have been the critical challenges for the gradual development of solid oxide fuel cells (SOFCs) in practical applications. The researchers all over the world attempt to develop alternative electrolyte materials with sufficient ionic conductivity. In this work, YSZ-CeO2 composite material was used as electrolytes in the construction of symmetrical SOFCs. The maximum power densities (Pmax) of YSZ-CeO2 based fuel cell can reach 680 mW cm-2 at 450 °C, 510 mW cm-2 at 430 °C, 330 mW cm-2 at 410 °C and even 200 mW cm-2 as the operational temperature was reduced to 390 °C. A series of characterizations indicates that the activation energy of the YSZ-CeO2 composite is significantly decreased, and the enhancement effect for ion conduction comes from interface transport. Our findings indicate the YSZ-CeO2 composite material can be a highly promising candidate for advanced low-temperature SOFC.

Enhancing the Performance of the p-n Heterostructure Electrolyte for Solid Oxide Fuel Cells via A-Site-Deficiency Engineering.

Semiconductor ionic electrolytes are attracting growing interest for developing low-temperature solid oxide fuel cells (LT-SOFCs). Our recent study has proposed a p-n heterostructure electrolyte based on perovskite oxide BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) and ZnO, achieving promising fuel cell performance. Herein, to further improve the performance of the heterostructure electrolyte, an A-site-deficiency strategy is used to solely modify BCFZY for regulating the ionic conduction and catalytic activity of the heterostructure. Two new electrolytes, B0.9CFZY-ZnO and B0.8CFZY-ZnO, were developed and systematically studied. The results show that the two samples gain improved ionic conductivity and auxiliary catalytic activity after A-site deficiency as a result of the increment of the surface and interface oxygen vacancies. The single cells with B0.9CFZY-ZnO and B0.8CFZY-ZnO exhibit enhanced peak power outputs at 450-550 °C compared to the cell based on B1.0CFZY-ZnO (typically, 745 and 795 vs 542 mW cm-2 at 550 °C). Particular attention is paid to the impact of A-site deficiency on the interface energy band alignment between BxCFZY and ZnO, which suggests that the p-n heterojunction effect of BxCFZY-ZnO for charge carrier regulation can be tuned by A-site deficiency to enable high proton transport while avoiding fuel cell current leakage. This study thus confirms the feasibility of A-site-deficiency engineering to optimize the performance of the heterostructure electrolyte for developing LT-SOFCs.

In Situ Formation of Ba3CoNb2O9/Ba5Nb4O15 Heterostructure in Electrolytes for Enhancing Proton Conductivity and SOFC Performance.

The in situ formation of a heterostructure delivers superior electrochemical properties as compared to the mechanical mixing, which shows great promise for developing new electrolytes for solid oxide fuel cells (SOFCs). Herein, in an SOFC constructed by the Ba5Nb4O15 electrolyte and Ni0.8Co0.15Al0.05LiO2-δ anode, an in situ formation of Ba3CoNb2O9/Ba5Nb4O15 heterostructure is designed by Co-ion diffusion from the anode to the electrolyte during cell operation, resulting in improved ion conductivity and fuel cell performance. An abnormal phenomenon is observed that the SOFC based on the Ba3CoNb2O9/Ba5Nb4O15 electrolyte delivered a peak power density of 703 mW/cm2 at 510 °C, which is higher than that at 550 °C. Characterization in terms of X-ray photoelectron spectroscopy and X-ray diffraction verifies that the operating temperature affected the Co doping concentrations, leading to different conducting behaviors of the heterostructure. Furthermore, it is found that the heterojunction of Ba3CoNb2O9 and Ba5Nb4O15 can restrict the electron migration to avoid current leakage of the cell and simultaneously enhance the proton conductivity. These findings manifest the developed in situ Ba3CoNb2O9/Ba5Nb4O15 heterostructure as a promising electrolyte for SOFCs.

Improving the electrochemical energy conversion of solid oxide fuel cells through the interface effect in La0.6Sr0.4Co0.2Fe0.8O3-δ-BaTiO3-δ electrolyte.

Herein, we present a heterostructure electrolyte with considerable potential for application in low-temperature solid oxide fuel cells (LT-SOFCs). Heterostructure electrolytes are advantageous because the multiphase interfaces in their heterostructures are superior for ion conduction than for bulk conduction. Most previous studies on heterostructure electrolytes explained the influence of interfacial parameters on ion conduction in terms of the space charge zones and lattice mismatch, neglecting the characterization of the interface. In this study, a series of heterostructure electrolytes comprising La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and BaTiO3-δ (BTO) with different composition ratios was developed. Further, the lattice mismatch due to thermal stress in this system was evaluated by thermal expansion and electron energy loss spectroscopy (EELS) analyses. Results indicated that 7LSCF-3BTO produced the narrowest interface and the most surface oxygen vacancies, suggesting that the stress generated by thermal expansion increased the density of the interface. The cell with the optimal 7LSCF-3BTO composition delivered a peak power density of 910mW cm-2 and an open circuit voltage of 1.07 V at 550 °C. The heterojunction effect was studied to elucidate the prevention of short circuiting in the LSCF-BTO cell, considering the Femi level and barrier energy height. This study provides novel ideas for the design of electrolytes for LT-SOFCs from the interface perspective.

LSCF-WO3 semiconductor composite electrolytes for low-temperature solid oxide fuel cells.

The La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)-WO3 semiconductor composite was applied as an electrolyte for low-temperature solid oxide fuel cells (LTSOFCs). The study results revealed that the fuel cell could output a maximum power density (P max) of 812 mW cm-2 when the weight ratio of LSCF to WO3 was 8 : 2 (8LSCF-2WO3), and its open-circuit voltage (OCV) was higher than 1.0 V. This indicated that there was no short circuit problem in this fuel cell device and 80 wt% LSCF existed in the electrolyte layer. This was mainly due to the suppressed electronic conductivity and increased ionic conductivity of the composite as compared with LSCF due to the introduction of the WO3 wide band semiconductor. The oxygen ionic conductivity of the 8LSCF-2WO3 electrolyte was 0.337 S cm-1, which is much higher than that of the pure LSCF material. According to the XPS analysis results, a higher oxygen vacancy content at the heterointerface between LSCF and WO3 contributed to the increased ionic conductivity.

Remarkable Ionic Conductivity in a LZO-SDC Composite for Low-Temperature Solid Oxide Fuel Cells.

Recently, appreciable ionic conduction has been frequently observed in multifunctional semiconductors, pointing out an unconventional way to develop electrolytes for solid oxide fuel cells (SOFCs). Among them, ZnO and Li-doped ZnO (LZO) have shown great potential. In this study, to further improve the electrolyte capability of LZO, a typical ionic conductor Sm0.2Ce0.8O1.9 (SDC) is introduced to form semiconductor-ionic composites with LZO. The designed LZO-SDC composites with various mass ratios are successfully demonstrated in SOFCs at low operating temperatures, exhibiting a peak power density of 713 mW cm-2 and high open circuit voltages (OCVs) of 1.04 V at 550 °C by the best-performing sample 5LZO-5SDC, which is superior to that of simplex LZO electrolyte SOFC. Our electrochemical and electrical analysis reveals that the composite samples have attained enhanced ionic conduction as compared to pure LZO and SDC, reaching a remarkable ionic conductivity of 0.16 S cm-1 at 550 °C, and shows hybrid H+/O2- conducting capability with predominant H+ conduction. Further investigation in terms of interface inspection manifests that oxygen vacancies are enriched at the hetero-interface between LZO and SDC, which gives rise to the high ionic conductivity of 5LZO-5SDC. Our study thus suggests the tremendous potentials of semiconductor ionic materials and indicates an effective way to develop fast ionic transport in electrolytes for low-temperature SOFCs.

Oxygen-Defect Enhanced Anion Adsorption Energy Toward Super-Rate and Durable Cathode for Ni-Zn Batteries.

The alkaline zinc-based batteries with high energy density are becoming a research hotspot. However, the poor cycle stability and low-rate performance limit their wide application. Herein, ultra-thin CoNiO2 nanosheet with rich oxygen defects anchored on the vertically arranged Ni nanotube arrays (Od-CNO@Ni NTs) is used as a positive material for rechargeable alkaline Ni-Zn batteries. As the highly uniform Ni nanotube arrays provide a fast electron/ion transport path and abundant active sites, the Od-CNO@Ni NTs electrode delivers excellent capacity (432.7 mAh g-1) and rate capability (218.3 mAh g-1 at 60 A g-1). Moreover, our Od-CNO@Ni NTs//Zn battery is capable of an ultra-long lifespan (93.0% of initial capacity after 5000 cycles), extremely high energy density of 547.5 Wh kg-1 and power density of 92.9 kW kg-1 (based on the mass of cathode active substance). Meanwhile, the theoretical calculations reveal that the oxygen defects can enhance the interaction between electrode surface and electrolyte ions, contributing to higher capacity. This work opens a reasonable idea for the development of ultra-durable, ultra-fast, and high-energy Ni-Zn battery.

The sintering temperature effect on electrochemical properties of Ce0.8Sm0.05Ca0.15O2-δ (SCDC)-La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) heterostructure pellet.

Recently, semiconductor-ionic materials (SIMs) have emerged as new functional materials, which possessed high ionic conductivity with successful applications as the electrolyte in advanced low-temperature solid oxide fuel cells (LT-SOFCs). In order to reveal the ion-conducting mechanism in SIM, a typical SIM pellet consisted of semiconductor La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and ionic conductor Sm and Ca Co-doped ceria Ce0.8Sm0.05Ca0.15O2-δ (SCDC) are suffered from sintering at different temperatures. It has been found that the performance of LSCF-SCDC electrolyte fuel cell decreases with the sintering temperature, the cell assembled from LSCF-SCDC pellet sintered at 600 °C exhibits a peak power density (Pmax) of 543 mW/cm2 at 550 °C and also excellent performance of 312 mW/cm2 even at LT (500 °C). On the contrary, devices based on 1000 °C pellet presented a poor Pmax of 106 mW/cm2. The performance difference may result from the diverse ionic conductivity of SIM pellet through different temperatures sintering. The high-temperature sintering could severely destroy the interface between SCDC and LSCF, which provide fast transport pathways for oxygen ions conduction. Such phenomenon provides direct and strong evidence for the interfacial conduction in LSCF-SCDC SIMs.

Advanced Fuel Cell Based on Perovskite La-SrTiO3 Semiconductor as the Electrolyte with Superoxide-Ion Conduction.

A solid oxide fuel cell's performance is largely determined by the ionic-conducting electrolyte. A novel approach is presented for using the semiconductor perovskite La0.25Sr0.75TiO3 (LST) as the electrolyte by creating surface superionic conduction, and the authors show that the LST electrolyte can deliver superior power density, 908.2 mW cm-2 at just 550 °C. The prepared LST materials formed a heterostructure, including an insulating core and a superionic conducting surface layer. The rapid ion transport along the surfaces or grain boundaries was identified as the primary means of oxygen ion conduction. The fuel cell-induced phase transition was observed from the insulating LST to a super O2- conductivity of 0.221 S cm-1 at 550 °C, leading to excellent current and power outputs.

Semiconductor-Ionic Nanocomposite La0.1Sr0.9MnO3-δ-Ce0.8Sm0.2O2-δ Functional Layer for High Performance Low Temperature SOFC.

A novel composite was synthesized by mixing La0.1Sr0.9MnO3-δ (LSM) with Ce0.8Sm0.2O2-δ (SDC) for the functional layer of low temperature solid oxide fuel cell (LT-SOFC). Though LSM, a highly electronic conducting semiconductor, was used in the functional layer, the fuel cell device could reach OCVs higher than 1.0 V without short-circuit problem. A typical diode or rectification effect was observed when an external electric force was supplied on the device under fuel cell atmosphere, which indicated the existence of a junction that prevented the device from short-circuit problem. The optimum ratio of LSM:SDC = 1:2 was found for the LT-SOFC to reach the highest power density of 742 mW·cm-2 under 550 °C The electrochemical impedance spectroscopy data highlighted that introducing LSM into SDC electrolyte layer not only decreased charge-transfer resistances from 0.66 Ω·cm² for SDC to 0.47⁻0.49 Ω·cm² for LSM-SDC composite, but also decreased the activation energy of ionic conduction from 0.55 to 0.20 eV.

Ethylene glycol adjusted nanorod hematite film for active photoelectrochemical water splitting.

We reported a facile adjusted method for the synthesis of high surface area nanorod hematite film as a photoanode for application in water splitting. Crystalline hematite nanorods (EG-α-Fe2O3) are fabricated by electrodeposition in Fe(2+) precursor solution with the addition of ethylene glycol (EG) and followed by annealing at 450 °C. The nanorod hematite film fabricated by the modified electrodeposition approach exhibits a more uncompact structure than α-Fe2O3 obtained by directly electrodepositing on the FTO substrate. The optical and structural characteristics of the obtained film are also tested. The results infer that EG can tune the morphology of hematite and improve the photoabsorption in the visible light region due to its inducement of one-dimensional growth of crystal hematite. It also enhances the photoresponse activity of hematite in water splitting by improving the activities at the semiconductor/solution interface. The photocurrent density of EG-α-Fe2O3 nanorods increased to 0.24 mA cm(-2) at 1.4 V vs. RHE in 1 M KOH (pH = 13.6), almost 5 times higher than the original α-Fe2O3 (0.05 mA cm(-2), measured under the same conditions).

Highly effective Ir(x)Sn(1-x)O2 electrocatalysts for oxygen evolution reaction in the solid polymer electrolyte water electrolyser.

We developed an advanced surfactant-assistant method for the Ir(x)Sn(1-x)O(2) (0 < x ≤ 1) nanoparticle (NP) preparation, and examined the OER performances by a series of half-cell and full-cell tests. In contrast to the commercial Ir black, the collective data confirmed the outstanding activity and stability of the fabricated Ir(x)Sn(1-x)O(2) (x = 1, 0.67 and 0.52) NPs, which could be ascribed to the amorphous structure, good dispersion, high pore volume, solid-solution state and Ir-rich surface for bi-metal oxides, and relatively large size (10-11 nm), while Ir(0.31)Sn(0.69) exhibited poor electro-catalytic activity because of the separated two phases, a SnO(2)-rich phase and an IrO(2)-rich phase. Furthermore, compared with highly active IrO(2), the improved durability, precious-metal Ir utilization efficiency and correspondingly reduced Ir loading were realized by the addition of Sn component. When the Ir(0.52)Sn(0.48)O(2) cell operated at 80 °C using Nafion® 115 membrane and less than 0.8 mg cm(-2) of the noble-metal Ir loading, the cell voltages we achieved were 1.631 V at 1000 mA cm(-2), and 1.821 V at 2000 mA cm(-2). The IR-free voltage at the studied current density was very close to the onset voltage of oxygen evolution. The only 50 µV h(-1) of voltage increased for the 500 h durability test at 500 mA cm(-2). In fact, these results are exceptional compared to the performances for OER in SPEWE cells known so far. This work highlights the potential of using highly active and stable IrO(2)-SnO(2) amorphous NPs to enhance the electrolysis efficiency, reduce the noble-metal Ir loading and thus the cost of hydrogen production from the solid polymer electrolyte water electrolysis.