RESUMEN
Ammonia, a vital component in the synthesis of fertilizers, plastics, and explosives, is traditionally produced via the energy-intensive and environmentally detrimental Haber-Bosch process. Given its considerable energy consumption and significant greenhouse gas emissions, there is a growing shift toward electrocatalytic ammonia synthesis as an eco-friendly alternative. However, developing efficient electrocatalysts capable of achieving high selectivity, Faraday efficiency, and yield under ambient conditions remains a significant challenge. This review delves into the decades-long research into electrocatalytic ammonia synthesis, highlighting the evolution of fundamental principles, theoretical descriptors, and reaction mechanisms. An in-depth analysis of the nitrogen reduction reaction (NRR) and nitrate reduction reaction (NitRR) is provided, with a focus on their electrocatalysts. Additionally, the theories behind electrocatalyst design for ammonia synthesis are examined, including the Gibbs free energy approach, Sabatier principle, d-band center theory, and orbital spin states. The review culminates in a comprehensive overview of the current challenges and prospective future directions in electrocatalyst development for NRR and NitRR, paving the way for more sustainable methods of ammonia production.
RESUMEN
Manganese (Mn)-based layer-structured transition metal oxides are considered as excellent cathode materials for potassium ion batteries (KIBs) owing to their low theoretical cost and high voltage plateau. The energy density and cycling lifetime, however, cannot simultaneously satisfy the basic requirements of the market for energy storage systems. One of the primary causes results from the complex structural transformation and transition metal migration during the ion intercalation and deintercalation process. The orbital and electronic structure of the octahedral center metal element plays an important role for maintaining the octahedral structural integrity and improving the K+ diffusivity by the introduced heterogeneous [Me-O] chemical bonding. A multitransition metal oxide, P3-type K0.5Mn0.85Co0.05Fe0.05Al0.05O2 (KMCFAO), was synthesized and employed as a cathode material for KIBs. Beneficial from the larger layer spacing for K+ to better accommodate and effectively preventing the irreversible structural transformation in the insertion/extraction process, it can reach a superior capacity retention up to 96.8% after 300 cycles at a current density of 500 mA g-1. The full cell of KMCFAO//hard carbon exhibits an encouraging promising energy density of 113.8 W h kg-1 at 100 mA g-1 and a capacity retention of 72.6% for 500 cycles.
