Lithium is the most attractive anode material for high-energy density rechargeable batteries, but its cycling is plagued by morphological irreversibility and dendrite growth that arise in part from its heterogeneous “native” solid electrolyte interphase (SEI). Enriching the SEI with lithium fluoride (LiF) has recently gained popularity to improve Li cyclability. However, the intrinsic function of LiF—whether chemical, mechanical, or kinetic in nature—remains unknown. Herein, we investigated the stability of LiF in model LiF-enriched SEIs that are either artificially preformed or derived from fluorinated electrolytes, and thus, the effect of the LiF source on Li electrode behavior. We discovered that the mechanical integrity of LiF is easily compromised during plating, making it intrinsically unable to protect Li. The ensuing in situ repair of the interface by electrolyte, either regenerating LiF or forming an extra elastomeric “outer layer,” is identified as the more critical determinant of Li electrode performance. Our findings present an updated and dynamic picture of the LiF-enriched SEI and demonstrate the need to carefully consider the combined role of ionic and electrolyte-derived layers in future design strategies.

A photostable p-type NiO photocathode based on a bifunctional cyclometalated ruthenium sensitizer and a cobaloxime catalyst has been created for visible-light-driven water reduction to produce H2. The sensitizer is anchored firmly on the surface of NiO, and the binding is resistant to the hydrolytic cleavage. The bifunctional sensitizer can also immobilize the water reduction catalyst. The resultant photoelectrode exhibits superior stability in aqueous solutions. Stable photocurrents have been observed over a period of hours. This finding is useful for addressing the degradation issue in dye-sensitized photoelectrochemical cells caused by desorption of dyes and catalysts. The high stability of our photocathodes should be important for the practical application of these devices for solar fuel production.

Proton reduction is one of the most fundamental and important reactions in nature. MoS2 edges have been identified as the active sites for hydrogen evolution reaction (HER) electrocatalysis. Designing molecular mimics of MoS2 edge sites is an attractive strategy to understand the underlying catalytic mechanism of different edge sites and improve their activities. Herein we report a dimeric molecular analogue [Mo2 S12 ](2-) , as the smallest unit possessing both the terminal and bridging disulfide ligands. Our electrochemical tests show that [Mo2 S12 ](2-) is a superior heterogeneous HER catalyst under acidic conditions. Computations suggest that the bridging disulfide ligand of [Mo2 S12 ](2-) exhibits a hydrogen adsorption free energy near zero (-0.05 eV). This work helps shed light on the rational design of HER catalysts and biomimetics of hydrogen-evolving enzymes.

No abstract

Electrochemical CO 2 conversion has a growing role to play in mitigating rising emissions and identifying novel end-uses for CO 2. We present a combined chemical-electrochemical process, facilitated by a novel electrolyte chemistry, that enables post-combustion CO 2 capture-conversion by integration of conventionally aqueous-based amine sorbents into a nonaqueous, alkali-based electrolyte. This combination imparts emergent discharge activity at high potentials of 3 V at a catalyst-free carbon electrode in a Li battery, advantageously combining two conventionally separate approaches to CO 2 mitigation.

p-Type dye-sensitized solar cells (p-DSCs) have attracted increasing attention recently, but they suffer from low fill factors (FFs) and unsatisfactory efficiencies. A full comprehension of the hole transport and recombination processes in the NiO p-DSC is of paramount importance for both the fundamental study and the practical device optimization. In this article, NiO p-DSCs were systematically probed under various bias and illumination conditions using electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent spectroscopy (IMPS), and intensity modulated photovoltage spectroscopy (IMVS). Under the constant 1 sun illumination, the recombination resistance (R rec ) of the cell deviates from an exponential relationship with the potential and saturates at ∼130 Ω cm 2 under the short circuit condition, which is ascribed to the overwhelming recombination with the reduced dye anions. Such a small R rec results in the small dc resistance, which decreases the "flatness" of the J−V curve. The quantitative analysis demonstrates that the FF value is largely attenuated by the recombination of holes in NiO with the reduced dyes. Our analysis also shows that if this recombination can be eliminated, then an FF value of 0.6 can be reached, which agrees with the theoretical calculation with a V oc of 160 mV.

We have systematically studied the effects of substitutional doping of p-type nanoparticulate NiO with cobalt ions. Thin films of pure and Co-doped NiO nanoparticles with nominal compositions Co(x)Ni(1-x)O(y) (0 ≤ x ≤ 0.1) were fabricated using sol-gel method. X-ray photoelectron spectroscopy revealed a surface enrichment of divalent cobalt ions in the Co(x)Ni(1-x)O(y) nanoparticles. Mott-Schottky analysis in aqueous solutions was used to determine the space charge capacitance values of the films against aqueous electrolytes, which yielded acceptor state densities (N(A)) and apparent flat-band potentials (E(fb)). Both N(A) and E(fb) values of the doped NiO were found to gradually increase with increasing amount of doping; thus the Fermi energy level of the charge carriers decreased with Co-doping. The photovoltage of p-DSCs constructed using the Co(x)Ni(1-x)O(y) films increased with increasing amount of cobalt, as expected from the trend in the E(fb). Co-doping increased both carrier lifetimes within the p-DSCs and the carrier transport times within the nanoparticulate semiconductor network. The nominal composition of Co₀.₀₆Ni₀.₉₄O(y) was found to be optimal for use in p-DSCs.

K anode is highly exothermic and energetically coupled with the H abstraction reaction between DME and O 2 − , which greatly promotes the DME decomposition. As a result, significant KO 2 and solvent decomposition products (KOH and K 2 CO 3 ) build up on the K anode surface. [21] This problem is even worse for K anode during battery cycling. The stripping and deposition of K metal in discharge-charge processes induce the constant formation of fresh K-ether interfaces, where the above mentioned side reactions are most favorable. Very recently, a few studies of stabilizing the metal anodes (mainly Li and Na) in metal-O 2 batteries have been reported, including using polymer membrane separator, coating a ceramic/polymer layer, or using surface treatment. [12,21,[24][25][26][27][28] Although these strategies mitigate the metal corrosion by O 2 crossover, they either rely on solvent wetting for ion conduction or are less effective for the highly reactive K metal. Therefore, the formation of a stable K/electrolyte interface to effectively protect the K metal from ether and O 2 molecules for improving the K-O 2 battery cycle stability is highly desirable yet very challenging.Here, we show that a solvent-and O 2 -impermeable layer can be formed in situ on K metal surface with 1 m potassium bis(trifluoromethanesulfonyl)imide (KTFSI) in ether electrolyte. It was found out that this protection layer is surprisingly effective in inhibiting the K anode decay by blocking ether molecules and O 2 crossover. As a result, the K-O 2 batteries have obtained excellent cycle stability over 60 cycles (≈700 h) even under pressurized O 2 environment (2 atm), which is over ten times better than that of the K-O 2 battery without the protection layer. This study highlights the importance of K anode protection and the potential of achieving long-life K anodes in K-O 2 batteries.The improved stability of K metal in ether solvents can be easily observed with the addition of KTFSI salt. Ether molecules are widely used in metal-air batteries owing to their better stability against superoxide intermediate attacks than carbonate electrolytes used in conventional Li-ion batteries. [5,29,30] However, in our previous studies, it is shown that DME, especially longer chain ether molecules (e.g., tetraglyme), can dissolve potassium metal through favorable oxygen coordination to K + , in agreement with the behavior reported before. [21,31] This phenomenon is featured by the generation of a characteristic blue color in the solvent. As shown in Figure 1a, tetraglyme solution would immediately take on a deep blue color once in contact with a piece of K metal under Argon environment. The blue color most likely comes from the solvated electrons (e solv − ), which are formed accompanying the chelation of K + ions by tetraglyme to keep the solution neutrally charged. The highly reactive e solv − can lead to CO bond reductive cleavages and therefore the tetraglyme solution had apparent color changes Lithium-oxygen (Li-O 2 ) batteries have been regarded as one of...