Hydrogen energy is an important direction of Chinese energy development strategy and an indispensable part of Chinese energy system. However, there are many problems in hydrogen storage and transportation, which limit the promotion and development of the hydrogen industry. Ammonia gas has the characteristics of zero carbon and high hydrogen content, with unique advantages in production, transportation, storage and safety. It is considered as one of the most promising hydrogen storage media. At the same time, it has a bright prospect in the direct power generation of solid oxide fuel cells as a fuel. In this paper, the research progress of ammonia fuel and direct ammonia solid oxide fuel cells is reviewed, with emphasis on the materials, system integration and long-term device stability. Accordingly, the future development of direct ammonia solid oxide fuel cells is prospected.

Aqueous zinc ion batteries have received a great deal of attention, due to their excellent safety and high-capacity density. However, zinc dendrites, which are prone to rapid growth in aqueous solutions, constitute an obvious obstacle to the development of aqueous zinc batteries. Conventional glass fiber separators are susceptible to dendrite penetration, owing to the poor structural stability. Porous YSZ ceramic sheets, with main pore size of about 6 μm and porosity up to 45.8887%, were developed by using porous ceramic preparation process. The stable pore structure of the porous YSZ ceramics effectively enhanced the cycle life of the battery. Specifically, the aqueous zinc ion battery based on the porous YSZ separators maintained a stable cycle of 763 h at a current density of 1 mA·cm^-2. Attempts have been tried to improve performances of the ceramic separator by using an interface modification method. It is finally found that weighing paper coated unilateral carbon could be used as the modification layer between the ceramic separator and the electrodes, further improving the cycle stability of the battery, while the composite ceramic separator symmetric batteries reached a cycle time of 1016 h. Stable ceramic pores and extremely low electronic conductivity effectively slow down the growth of Zn dendrites, while the solid and conductive interface modification layer played an important role in homogenizing the distribution of the interfacial electric field.Therefore, such composite ceramic separators showed excellent stability of aqueous ion batteries.

High fracture strength and excellent thermal stability of ion-conducting ceramic materials are important factors for solving the thermal runaway problem currently plaguing the development of alkali-metal batteries, but the high ion-transport resistance they exhibit at room temperature limits the practical performance of all-solid-state batteries. Na-β"-Al₂O₃ (SBA), an ionic conductor ceramics, with a unique layered two-dimensional Na⁺ conduction structure, is explored. LaNbO₄ ceramics with "microelastic" characteristics were synthesized as the second phase to fill and modify the grain gap of SBAs to increase their room temperature ionic conductivity. In the experiment, 0.50 wt.% LaNbO₄ is optimal in terms of enhancement effect, with a room temperature ionic conductivity of 2.061 mS·cm^-1. The activation energy of the doped SBA was also reduced to 0.1545 eV from 0.1714 eV for the pure phase SBA. SEM images of the ceramic cross-section showed that the appropriate content of LaNbO₄ not only enhanced the sintering behavior of the SBAs, but also boosted the crystallization of the SBAs, thus leading to a reduction in the impedance. Symmetric all-solid-state sodium batteries assembled with the doped SBAs could be operated at lower voltages in constant-current charge/discharge at room temperature.

In recent years, sodium-ion solid-state batteries have gradually attracted attentions as a member of rechargeable batteries. In solid-state batteries, liquid electrolytes are avoided, thus diminishing the risks such as leakage and explosion. At present, it is still a challenge to increase the ionic conductivity of solid-state electrolytes. In this study, Zr⁴⁺ was introduced into Na₅YSi₄O₁₂ (NYS), where NaNO₃, YN₃O₉·6H₂O, C₈H₂₀O₄Si and ZrO(NO₃)₂·xH₂O were used as starting materials. A solution-assisted solid-phase reaction method (SASSR) was employed to prepare the solid electrolytes Na_5-xY_1-xZr_xSi₄O₁₂ (x=0.04, 0.06, 0.08, 0.10, 0.12) with hexagonal crystal structure. The effect of Zr⁴⁺ on ionic conductivity of Na_5-xY_1-xZr_xSi₄O₁₂ (NYZS) was studied, while the maximum ionic conductivity of 2.13 mS·cm^-1 was achieved at x=0.08, with an activation energy of 0.222 eV. Compared with that of NYS, the conductivity of NYZS is greatly increased, due to the presence of sodium vacancies after Zr⁴⁺ doping. In summary, Na_5-xY_1-xZr_xSi₄O₁₂ is a competitive sodium-ion solid-state electrolyte, which is expected to become promising candidate for new generation of energy conversion.

Although sodium-ion solid electrolytes have been studied for many years, their low conductivity at room temperature and an order of magnitude gap with organic liquid electrolytes are the main obstacles limiting their practical application. In this paper, high performance Na₅YSi₄O₁₂ solid electrolytes with hexagonal crystal structure were prepared by using solution-assisted solid-state reaction (SASSR) method, with NaNO₃, YN₃O₉·6H₂O and C₈H₂₀O₄Si as raw materials. The relationship between sintering temperature and dwelling time and ionic conductivity of Na₅YSi₄O₁₂ (NYS) were focused. The sample sintered at 1050 ℃ for 6 h had the highest ionic conductivity of 1.52 mS·cm^-1, with an activation energy of 0.215 eV.Compared with that of the one prepared with the commercial solid-phase reaction method, conductivity of the material in this work has been greatly improved. The increase in conductivity is attributed to the high sintering activity of the Na₅YSi₄O₁₂ powder and the unique 3D transport channel. The charge carriers can be transported along the channel or across different channels, thus leading to a higher conductivity.