Most current research is devoted to electrochemical nitrate reduction reaction for ammonia synthesis under alkaline/neutral media while the investigation of nitrate reduction under acidic conditions is rarely reported. In this work, we demonstrate the potential of TiO₂ nanosheet with intrinsically poor hydrogen-evolution activity for selective and rapid nitrate reduction to ammonia under acidic conditions. Hybridized with iron phthalocyanine, the resulting catalyst displays remarkably improved efficiency toward ammonia formation owing to the enhanced nitrate adsorption, suppressed hydrogen evolution and lowered energy barrier for the rate-determining step. Then, an alkaline-acid hybrid Zn-nitrate battery was developed with high open-circuit voltage of 1.99 V and power density of 91.4 mW cm^–2. Further, the environmental sulfur recovery can be powered by above hybrid battery and the hydrazine-nitrate fuel cell can be developed for simultaneously hydrazine/nitrate conversion and electricity generation. This work demonstrates the attractive potential of acidic nitrate reduction for ammonia electrosynthesis and broadens the field of energy conversion.

Increasing emissions of carbon dioxide and the depletion of finite fossil fuels have led to many concerns about global warming and energy crises. Consequently, a sustainable and alternative method, photocatalytic CO₂ reduction to chemical fuels has received considerable attention. This perspective highlights recent knowledge and the main challenges in CO₂ photoreduction primarily from the theoretical field. The fundamental understanding of CO₂ adsorption and reaction mechanism at an atomic level is fully addressed, and the relevant effects dominating the process of CO₂ photoreduction are also elucidated. Moreover, recent development of photocatalysts including structural modification is presented, which greatly affects the efficiency and selectivity of CO₂ conversion. Finally, the possibilities and challenges in this field are discussed.

More lithium disorder is present in meta-stable AA-stackings during delithiation.