Inactive lithium (Li) formation is the immediate cause of capacity loss and catastrophic failure of Li metal batteries. However, the chemical component and the atomic level structure of inactive Li have rarely been studied due to the lack of effective diagnosis tools to accurately differentiate and quantify Li + in solid electrolyte interphase (SEI) components and the electrically isolated unreacted metallic Li 0 , which together comprise the inactive Li. Here, by introducing a new analytical method, Titration Gas Chromatography (TGC), we can accurately quantify the contribution from metallic Li 0 to the total amount of inactive Li. We uncover that the Li 0 , rather than the electrochemically formed SEI, dominates the inactive Li and capacity loss. Using cryogenic electron microscopies to further study the microstructure and nanostructure of inactive Li, we find that the Li 0 is surrounded by insulating SEI, losing the electronic conductive pathway to the bulk electrode. Coupling the measurements of the Li 0 global content to observations of its local atomic structure, we reveal the formation mechanism of inactive Li in different types of electrolytes, and identify the true underlying cause of low Coulombic efficiency in Li metal deposition and stripping. We ultimately propose strategies to enable the highly efficient Li deposition and stripping to enable Li metal anode for next generation high energy batteries. Main Text:To achieve the energy density of 500 Wh/kg or higher for next-generation battery technologies, Li metal is the ultimate anode, because it is the lightest metal on earth (0.534 g cm -3 ), delivers ultra-high theoretical capacity (3860 mAh g -1 ), and has the lowest negative electrochemical potential (-3.04 V vs. SHE) 1 . Yet, Li metal suffers from dendrite growth and low Coulombic efficiency (CE) which have prevented the extensive adoption of Li metal batteries (LMBs) 2-4 . Since the first demonstration of a Li metal battery in 1976 5 , tremendous effort has been made in preventing dendritic Li growth and improving CE, including electrolyte engineering 6-9 , interface protection 10 and substrate architecture 11 . While dense Li can be achieved without any dendrites during the plating process, the stripping process will eventually dominate the CE thus the reversibility of Li metal anode.The formation of inactive Li, also known as "dead" Li, is the immediate cause of low CE, short cycle life and violent safety hazard of LMBs. It consists of both (electro)chemically formed Li + compounds

Engineering catalytic sites at the atomic level provides an opportunity to understand the catalyst’s active sites, which is vital to the development of improved catalysts. Here we show a reliable and tunable polyoxometalate template-based synthetic strategy to atomically engineer metal doping sites onto metallic 1T-MoS 2 , using Anderson-type polyoxometalates as precursors. Benefiting from engineering nickel and oxygen atoms, the optimized electrocatalyst shows great enhancement in the hydrogen evolution reaction with a positive onset potential of ~ 0 V and a low overpotential of −46 mV in alkaline electrolyte, comparable to platinum-based catalysts. First-principles calculations reveal co-doping nickel and oxygen into 1T-MoS 2 assists the process of water dissociation and hydrogen generation from their intermediate states. This research will expand on the ability to improve the activities of various catalysts by precisely engineering atomic activation sites to achieve significant electronic modulations and improve atomic utilization efficiencies.

Although ammonia borane (NH 3 BH 3 ,A B) has been identified as an excellent hydrogen-storage medium, the development of a highly active catalystt hat can function under mild conditions for controllable hydrogen release is still ag reat challenge. The synergistic effect induced by interactions between metal nanoparticles and asupport has been widely applied in thermocatalytic conversion processes. In this work, Pd nanoparticles (NPs) highly dispersed on hollow NiCol ayered double hydroxide (LDH) wered esigned for efficient hydrogen generation from AB at room temperature. During the hydrolytic dehydrogenation of AB, Pd/a-LDH and Pd/b-LDHe xhibited catalytic activities with total turnover frequency (TOF) values of 49.5 and 28.1 min À1 with activation energy (E a )v alues of 20.56 and 37.56 kJ mol À1 ,r espectively,a t2 98 K; thus, these catalysts outperform mostP d-based catalysts. The improved catalytic effect was attributedt ot he controllable size and fine distribution of the Pd NPs and the collaborative effect provided by the hydroxide of a-LDH and the intercalated anions( HO À ). This catalysts design principle can be easily transferred to other catalyst research fields for energy-conversion and -storage purposes.Hydrogen is the simplest and cleanest fuel carrier and is usually utilized in af uel-cell setup to generate power;i tp roduces only water and heat as byproducts. [1,2] Hydrogenp roduces the highest energy per mass amonga ny fuel. Unfortunately,o wing to its low volumetric density under ambient conditions, the major obstacle that prevents the building of hydrogen economy is the development of advanced storagem ethods that have the potentialf or highere nergy density per volume. [3][4][5] Subsequently,i ti sa lso important to develop technologiest hat can release hydrogen in ac ontrollable fashion under mild conditions from said medium. Chemical hydrides are promising candidates owing to their high gravimetric hydrogen densities and favorable thermodynamic and kinetic properties towards dehydrogenation. [6,7] Among them, ammonia borane (NH 3 BH 3 , AB) is considered to be an efficient carrier,w ith superbstability in aqueous and methanol solutions, ah igh volumetric density of 146 gL À1 ,a nd ah ydrogen capacity of 196 gkg À1 . [8,9] Hydrogen stored in AB can be releasedbyeither thermaldecomposition or solvolysis. [10,11] Considering the high energy input of thermald ecomposition (> 100 8C), much research has been focused on the hydrolytic dehydrogenationo fA B[ Eq. (1)] in the presence of metal catalysts under ambient conditions. [12] Hundreds of metal catalysts have been exploited to promote the efficiency of AB dehydrogenation. [13] Amongt hem, Pd nanoparticle (NP)-based catalytic systems serve as favorable catalysts for the hydrolysiso fA Bb ecause they are cheaper than other precious metals and have higher activity than nonnoble metal catalysts. [14,15] It is well known that although smallsized metal NPs can provide more catalytic active sites, such NPs usuallys uffer from deactivation and inst...

Nitrate and nitrite (NO x –) are widespread contaminants in industrial wastewater and groundwater. Sustainable ammonia (NH3) production via NO x – electroreduction provides a prospective alternative to the energy-intensive industrialized Haber–Bosch process. However, selectively regulating the reaction pathway, which involves complicated electron/proton transfer, toward NH3 generation relies on the robust catalyst. A specific consideration in designing selective NO x –-to-NH3 catalysts should meet the criteria to suppress competing hydrogen evolution and avoid the presence of neighboring active sites that are in favor of adverse N–N coupling. Nevertheless, efforts in this regard are still inadequate. Herein, we demonstrate that isolated ruthenium sites can selectively reduce NO x – into NH3, with maximal Faradaic efficiencies of 97.8% (NO2 – reduction) and 72.8% (NO3 – reduction) at −0.6 and −0.4 V, respectively. Density functional theory calculations simulated the reaction mechanisms and identified the *NO → *NOH as the potential rate-limiting step for NO x –-to-NH3 conversion on single-atom Ru sites.

Current artificial photosynthesis (APS) systems are promising for the storage of solar energy via transportable and storable fuels, but the anodic half-reaction of water oxidation is an energy intensive process which in many cases poorly couples with the cathodic half-reaction. Here we demonstrate a self-sustaining microbial photoelectrosynthesis (MPES) system that pairs microbial electrochemical oxidation with photoelectrochemical water reduction for energy efficient H generation. MPES reduces the overall energy requirements thereby greatly expanding the range of semiconductors that can be utilized in APS. Due to the recovery of chemical energy from waste organics by the mild microbial process and utilization of cost-effective and stable catalyst/electrode materials, our MPES system produced a stable current of 0.4 mA/cm for 24 h without any external bias and ∼10 mA/cm with a modest bias under one sun illumination. This system also showed other merits, such as creating benefits of wastewater treatment and facile preparation and scalability.