A critical current density on stripping (CCS) is identified that results in dendrite formation on plating and cell failure. When the stripping current density removes lithium from the interface faster than it can be replenished, voids form in the lithium at the interface and accumulate on cycling increasing the local current density at the interface and ultimately leading to dendrite formation on plating, short-circuit and cell death. This occurs even when the overall current density is significantly below the threshold for dendrite formation on plating. For the Li / Li6PS5Cl / Li cell, this is 0.2 and 1 mA•cm -2 at 3 and 7 MPa pressure respectively, compared with a critical current for plating of 2 mA•cm -2 at both 3 and 7 MPa. The pressure dependence on stripping indicates creep rather than Li diffusion is the dominant mechanism transporting Li to the interface. The critical stripping current is a major factor limiting the power density of lithium anode solid state cells. Significant pressure may be required to achieve even modest power densities in solid state cells.

Lithium dendrite (filament) propagation through ceramic electrolytes, leading to short-circuits at high rates of charge, is one of the greatest barriers to realising high energy density all-solidstate lithium anode batteries. Utilising in-situ X-ray computed tomography coupled with spatially mapped X-ray diffraction, the propagation of cracks and the propagation of lithium dendrites through the solid electrolyte have been tracked in a Li/Li6PS5Cl/Li cell as a function of the charge passed. On plating, cracking initiates with spallation, conical "pothole"-like cracks that form in the ceramic electrolyte near the surface with the plated electrode. The spallations form predominantly at the lithium electrode edges where local fields are high. Transverse cracks then propagate from the spallations across the electrolyte from the plated to the stripped electrode. Lithium ingress drives the propagation of the spallation and transverse cracks by widening the crack from the rear, i.e. the crack front propagates ahead of the Li. As a result, cracks traverse the entire electrolyte before the Li arrives at the other electrode and therefore before a short-circuit occurs.

Delaminated carbon nitride nanosheets were prepared by high-temperature H2 treatment of bulk carbon nitride with defects being introduced during this treatment. Although the defects can act as traps for charge carriers, reducing photoluminescence lifetime, they also form highly active photocatalytic sites for hydrogen evolution. The nanostructured materials exhibit substantially enhanced photocatalytic activity due to a synergistic effect between delamination, the presence of defects, and associated band gap changes.

An advantageous solid electrolyte/liquid electrolyte interface is crucial for the implementation of a protected lithium anode in liquid electrolyte cells. Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZTO) garnet electrolytes are among the few solid electrolytes that are stable in contact with lithium metal. We show LLZTO is unstable in contact with the organic carbonate-based Li + liquid electrolyte used in conventional Li-ion cells. The interfacial resistance between LLZTO and LiPF 6 in (CH 2 O) 2 CO: OC(OCH 3 ) 2 (1:1 v/v) increases with time due to the growth of a lithium-ion-conducting solid electrolyte interphase (SEI) at the surface of the ceramic electrolyte. The interphase is composed of Li 2 CO 3 , LiF, Li 2 O, and organic carbonates. Even at a rate of 5 mA cm À2 , a 3 V potential drop occurs across the LLZTO/liquid electrolyte interface. A practical LLZTO membrane (thickness $10 mm), in contact with a lithium anode, gives a potential loss of $16 mV, less than 1% of the resistance of the SEI.

Three-electrode studies coupled with tomographic imaging of the Na/Na-β″-alumina interface reveal that voids form in the Na metal at the interface on stripping and they accumulate on cycling, leading to increasing interfacial current density, dendrite formation on plating, short circuit, and cell failure. The process occurs above a critical current for stripping (CCS) for a given stack pressure, which sets the upper limit on current density that avoids cell failure, in line with results for the Li/solid-electrolyte interface. The pressure required to avoid cell failure varies linearly with current density, indicating that Na creep rather than diffusion per se dominates Na transport to the interface and that significant pressures are required to prevent cell death, >9 MPa at 2.5 mA·cm–2.

All-solid-state batteries with a Li anode and ceramic electrolyte have the potential to deliver a step change in performance compared with today's Li-ion batteries 1,2 . However, Li dendrites (filaments) form on charging at practical rates, penetrate across the ceramic electrolyte leading to short-circuit and cell failure 3,4 . Previous models of dendrite penetration have generally focused on a single process for dendrite initiation and propagation, with Li driving the crack at its tip [5][6][7][8][9] . Here we show that initiation and propagation are separate processes.

Multivalent cation rechargeable batteries, including those based on Ca, Mg, Al, etc., have attracted considerable interest as candidates for beyond Li-ion. Recent developments have realized promising electrolyte compositions for rechargeable Ca batteries; however, an in-depth understanding of the Ca plating and stripping behavior, and the mechanisms by which adverse dendritic growth may occur, remains underdeveloped. In this work, via in-situ transmission electron microscopy, we have captured the real-time nucleation, growth, and dissolution of Ca, the formation of dead Ca, and demonstrated the critical role of current density and the solid-electrolyte interphase layer in controlling the plating morphology. In particular, the interface was found to influence Ca deposition morphology, and can lead 2 to Ca dendrite growth under unexpected conditions. These observations allow us to propose a model explaining the preferred conditions for reversible and efficient Ca plating.Multivalent cation batteries based on Mg, Ca, Al, etc. have attracted significant interest as potential candidates to replace Li-ion batteries in recent years. [1][2][3][4][5] These metallic anodes have much higher natural metal abundancy, and are reported to be much less prone to dendrite formation compared with metallic Li anode, [3][4][5][6][7][8][9][10][11] potentially due to their lower self-diffusion barriers. 1,12,13 The Ca-ion system has demonstrated significant potential. It has a comparable volumetric capacity to Li, and compared with other multivalent systems like Mg, it also has the advantages of higher earth abundance, lower reductive potential and lower charge density. 1 Despite this, the development of Ca-ion batteries has been slow in part due to issues with the anode, where most studied electrolytes react with metallic Ca, rapidly forming surface passivation layers comprised of CaCl2, Ca(OH)2, or CaCO3, that block Ca ion diffusion and make further plating impossible. [14][15][16][17] However, recent breakthroughs in electrolyte research have brought renewed interest in Ca-ion batteries. [18][19][20][21] These works have demonstrated promising Ca-based electrolytes that are capable of continuous plating and stripping with relatively high efficiency at moderately elevated 17 or room-temperatures. 4,11,22 While most previous studies demonstrated fairly smooth plating morphology, [3][4][5][6][7][8][9][10][11] a recent paper by Davidson et al. 23 showed that dendrites do grow in Mg-ion electrolyte. This challenges the widely accepted belief that multivalent systems do not form dendrites easily. Since research into Ca-ion electrolytes is at an early stage, little work has been done to systematically study their plating and stripping processes. This study explores the electroplating morphology and mechanism within the Ca-ion system via in situ transmission electron microscopy (TEM) to evaluate the feasibility of employing metallic Ca anodes, and to provide a deeper understanding of this system for future optimization.

Precious metal-titania materials make good catalysts for hydrogen production from a variety of organic substrates using sunlight. These substrates essentially act as reductants for water, by intercepting electrophilic oxygen species generated by electron-hole excitation resulting from photon absorption in the titania support. As a result, the hydrogen produced comes partly from water splitting and partly from dehydrogenation of the organic substrate. Why only precious metals work for the reaction is discussed, together with the mechanism of these reactions. The oxygenate substrates are decarbonylated to produce adsorbed CO, which is removed in the presence of light by the electrophilic oxygen as CO 2 , but the level of CO 2 detected is strongly affected by the amount of liquid water present, due to absorption and reaction to form carbonic acid. The possibilities for application of this technology in the domestic environment, the 'Photocatalytic Window' is considered.Keywords Photo-catalysis Á Photo-reforming Á Water splitting Á Hydrogen production Á Methanol Setting the SceneThe human race is in a period of fast transition in all sorts of aspects of life. Perhaps the most important of these is the changing energy scene. Because of the increase in population and increased industrialisation the most convenient forms of useable energy that are available in large quantity, fossil fuels, have been utilized for energy supply. These are firstly coal, used originally for driving steam generation for the new steam engines invented and widely introduced for manufacturing and transport in England from the late 18th century. Following from this came the widespread use of crude oil for transport, in the form of refined petroleum spirit, and in more recent times increasing use of gas powered electrical power generation and domestic combustion. As a result there has been an increase of CO 2 in the atmosphere-increasing from the geologically steady value of about 280 ppm, now just breaking the 400 ppm level, a 42 % increase. The source of these increases can be traced back to the original industrialisation of the early-mid 18th century. Figure 1 illustrates this in terms of the CO 2 level in the atmosphere, combined with a derivative which traces the start of this increase to the period just after the development of more efficient forms of steam engines for mechanical power generation see Ref. [1].The consequences of this geologically fast increase in CO 2 levels can be debated, but what is absolutely certain is that, as sentient beings, humans should not be playing with dice by abnormal perturbance of natural equilibrium, over a geologically fast timescale. The results are not likely to be positive for the planet, except in the sense that it might help reduce the human population.Thus there is an urgent need to stop the CO 2 increase and to find new sustainable ways of fuelling our future. Of course we have a number of successful technologies in Electronic supplementary material The online version of this article