The fundamental kinetics of the electrocatalytic sulfur reduction reaction (SRR), a complex 16-electron conversion process in lithium-sulfur batteries, is insufficiently explored to date. Herein, by directly profiling the activation energies in the multi-step SRR, we reveal that the initial reduction of sulfur to the soluble polysulfides is relatively easy with low activation energy, while the subsequent conversion of the polysulfides into the insoluble Li 2 S 2 /Li 2 S is more difficult with much higher activation energy, which contribute to the accumulation of polysulfides and exacerbate the polysulfide shuttling effect. We use heteroatom-doped graphene as a model system to explore electrocatalytic SRR. We show nitrogen and sulfur dual-doped graphene considerably reduces the activation energy to improve SRR kinetics. Density functional calculations confirm that the doping tunes the p-band center of the active carbons for an optimal adsorption strength of intermediates and electroactivity. This study establishes electrocatalysis as a promising pathway to high performance lithium-sulfur batteries. The sulfur reduction reaction (SRR) in lithium-sulfur (Li-S) chemistry undergoes a complex 16-electron conversion process, transforming S 8 ring molecules into a series of soluble lithium polysulfides (LiPSs) with variable chain lengths before fully converting them into 2 insoluble Li 2 S 2 /Li 2 S products. This 16-electron SRR process is of considerable interest for high-density energy storage with theoretical capacity of 1672 mAh g-1 , but the chemistry is plagued by sluggish sulfur reduction kinetics and polysulfide (PS) shuttling effect. In practical Li-S cells, these effects limit the rate capability and cycle life 1,2. These limitations are fundamentally associated with the slow and complex reduction reaction involving S 8 ring molecules. In general, the insulating nature of elemental sulfur and its reduced products, and the sluggish charge transfer kinetics lead to incomplete conversion of S 8 molecules to soluble LiPSs. These polysulfides may shuttle across the separator to react with and deposit on the lithium anode, resulting in rapid capacity fading 3. Considerable efforts have been devoted to combating the PS shuttling effect, typically by employing a passive strategy by using various sulfur host materials to physically or electrostatically trap the LiPSs in the cathode structure 4-13. These passive confinement/entrapping strategies have partly mitigated the PS shuttling

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Energy devices such as rechargeable batteries, fuel cells, and solar cells are central to powering a renewable, mobile, and electrified future. To advance these devices requires a fundamental understanding of the complex chemical reactions, material transformations, and charge flow that are associated with energy-conversion processes. Analytical in situ transmission electron microscopy (TEM) offers a powerful tool for directly visualizing these complex processes at the atomic scale in real time and in operando. Recent advancements in energy materials and devices that have been enabled by in situ TEM are reviewed. Firstly, the evolutionary development of TEM nanocells from the open-cell configuration to the close-cell, and finally the full-cell, design is reviewed. Next, in situ TEM studies of rechargeable ion batteries in a practical operation environment are explored, followed by applications of TEM for in situ observation of electrocatalyst formation, evolution, and degradation in proton-exchange-membrane fuel cells, and investigations of new energy materials such as perovskites for solar cells through in situ TEM. Finally, recent advances in the use of environmental TEM and cryogenic electron microscopy in probing clean-energy materials are presented and emerging opportunities and challenges in in situ TEM research of energy materials and devices are discussed.

Hydrogen electrochemistry on platinum low-index single-crystal surfaces in alkaline solution.

Here, we report a straightforward approach to synthesize hierarchical porous carbons (HPCs) via a high-temperature ionothermal synthesis and partial pyrolysis of covalent triazine frameworks (CTFs) in molten ZnCl2. By using 1,4-dicyanobenzene (DCB), 1,3-dicyanobeznene (mDCB), or 2,6-dicyanopyridine (DCP) as the monomer precursors for the CTFs, we found that ZnCl2 acts as an effective porogen in the system from monomers with weak solvent–solute interactions (DCB and mDCB). The resulting HPCs derived from DCB and mDCB exhibit a systematically tunable hierarchical porosity with an average pore size ranging from 2.5–8.0 nm, by varying the concentration of monomers in solution. We show a decreasing DCB to ZnCl2 ratio gives rise to larger mesopores, with improved pore connectivity and accessibility that is beneficial to mass transport and ion diffusion for high performance electric double layer capacitors (EDLCs) at high mass loadings. We demonstrate EDLCs with specific capacity values over 155 F/g at high mass loadings of 15 mg/cm2, delivering exceptional areal capacities of over 2.27 F/cm2 at low rates and 1.48 F/cm2 at high rates.