Driving the sodium-oxygen battery chemistry towards the efficient formation of discharge products: The importance of sodium superoxide quantification

Sodium-oxygen batteries(SOBs) have the potential to provide energy densities higher than the state-ofthe-art Li-ion batteries. However, controlling the formation of sodium superoxide(NaO_(2)) as the sole discharge product on the cathode side is crucial to achieve durable and efficient SOBs. In this work, the discharge efficiency of two graphene-based cathodes was evaluated and compared with that of a commercial gas diffusion layer. The discharge products formed at the surface of these cathodes in a glyme-based electrolyte were carefully studied using a range of characterization techniques. NaO_(2) was detected as the main discharge product regardless of the specific cathode material while small amounts of Na_(2)O_(2).2H_(2)O and carbonate-like side-products were detected by X-ray diffraction as well as by Raman and infrared spectroscopies. This work leverages the use of X-ray diffraction to determine the actual yield of NaO_(2)which is usually overlooked in this type of batteries. Thus, the proper quantification of the superoxide formed on the cathode surface is widely underestimated;even though is crucial for determining the efficiency of the battery while eliminating the parasitic chemistry in SOBs. Here, we develop an ex-situ analysis method to determine the amount of NaO_(2) generated upon discharge in SOBs by transmission X-ray diffraction and quantitative Rietveld analysis. This work unveils that the yield of NaO_(2) depends on the depth of discharge where high capacities lead to very low discharge efficiency, regardless of the used cathode. We anticipate that the methodology developed herein will provide a convenient diagnosis tool in future efforts to optimize the performance of the different cell components in SOBs.

Colloidal quantum dot for infrared-absorbing solar cells:State-oftheart and prospects

Colloidal quantum dot(CQD)shows great potential for application in infrared solar cells due to the simple synthesis techniques,tunable infrared absorption spectrum,and high stability and solution-processability.Thanks to significant efforts made on the surface chemistry of CQDs,device structure optimization,and device physics of CQD solar cells(CQDSCs),remarkable breakthroughs are achieved to boost the infrared photovoltaic performance and stability of CQDSCs.In particular,the CQDSC with a high power conversion efficiency of~14%and good stability is reported,which is very promising for infrared-absorbing solar cells.In this review,we highlight the unique optoelectronic properties of CQDs for the development of infrared-absorbing solar cells.Meanwhile,the latest advances in finely controlling surface properties of CQDs are comprehensively summarized and discussed.Moreover,the device operation of CQDSCs is discussed in-depth to highlight the impact of the device structure optimization of CQDSCs on their photovoltaic performance,and the emerging novel types of CQDSCs,such as semitransparent,flexible,and lightweight CQDSCs,are also demonstrated.The device stability of CQDSCs is also highlighted from the viewpoint of practical applications.Finally,the conclusions and possible challenges and opportunities are presented to promote the development steps of the CQDSCs with higher infrared photovoltaic performance and robust stability.

Influence of O-O formation pathways and charge transfer mediator on lipid bilayer membrane-like photoanodes for water oxidation

Inspired by the function of crucial components in photosystemⅡ(PSⅡ),electrochemical and dyesensitized photoelectrochemical(DSPEC)water oxidation devices were constructed by the selfassembly of well-designed amphipathic Ru(bda)-based catalysts(bda=2,2'-bipyrdine-6,6'-dicarbonoxyl acid)and aliphatic chain decorated electrode surfaces,forming lipid bilayer membrane(LBM)-like structures.The Ru(bda)catalysts on electrode-supported LBM films demonstrated remarkable water oxidation performance with different O-O formation mechanisms.However,compared to the slow charge transfer process,the O-O formation pathways did not determine the PEC water oxidation efficiency of the dyesensitized photoanodes,and the different reaction rates for similar catalysts with different catalytic paths did not determine the PEC performance of the DSPECs.Instead,charge transfer plays a decisive role in the PEC water oxidation rate.When an indolo[3,2-b]carbazole derivative was introduced between the Ru(bda)catalysts and aliphatic chain-modified photosensitizer in LBM films,serving as a charge transfer mediator for the tyrosine-histidine pair in PSⅡ,the PEC water oxidation performance of the corresponding photoanodes was dramatically enhanced.

CO oxidation on MXene(Mo_(2)CS_(2)) supported single-atom catalyst: A termolecular Eley-Rideal mechanism

Finding transition metal catalysts for effective catalytic conversion of CO to CO_(2)has attracted much attention.MXene as a new 2D layered material of early transition metal carbides,nitrides,and carbo-nitrides is a robust support for achoring metal atoms.In this study,the electronic structure,geometries,thermodynamic stability,and catalytic activity of MXene (Mo_(2)CS_(2)) supported single noble metal atoms (NM=Ru,Rh,Pd,Ir,Pt and Au) have been systematically examined using first-principles calculations and ab initio molecular dynamic (AIMD) simulations.First,AIMD simulations and phonon spectra demonstrate the dynamic and thermal stabilities of Mo_(2)CS_(2)monolayer.Three likely reaction pathways,LangmuirHinshelwood (LH),Eley-Rideal (ER),and Termolecular Eley–Rideal (TER) for CO oxidation on the Ru1-and Ir_(1)@Mo_(2)CS_(2)SACs,have been studied in detail.It is found that CO oxidation mainly proceeds via the TER mechanism under mild reaction conditions.The corresponding rate-determining steps are the dissociation of the intermediate (OCO-Ru_(1)-OCO) and formation of OCO-Ir_(1)-OCO intermediate.The downshift d-band center of Ru1-and Ir_(1)@Mo_(2)CS_(2)help to enhance activity and improve catalytst stability.Moreover,a microkinetic study predicts a maximum CO oxidation rate of 4.01×10^(2)s^(-1)and 4.15×10^(3)s^(-1)(298.15K) following the TER pathway for the Ru_(1)-and Ir_(1)@Mo_(2)CS_(2)catalysts,respectively.This work provides guideline for fabricating and designing highly efficient SACs with superb catalyts using MXene materials.

Photo-Induced Water Oxidation Based on a Mononuclear Cobalt(II)Complex

Photo-induced water oxidation based on first row transition metal complexes has drawn much attention recently as a part of the efforts to design systems for solar fuel production.Here,the classic tetradentate ligand TPA(tris(2-pyridylmethyl)amine)is used together with cobalt(II)in CH_(3)CN to form a mononuclear cobalt complex[Co(TPA)Cl]Cl.Single crystal X-ray diffraction shows that[Co(TPA)Cl]Cl is composed of discrete cationic units with a penta-coordinate cobalt center,along with chloride counter ions.In borate buffer,the Co complex acts as a water oxidation catalyst,as shown by the presence of a catalytic wave in electrochemistry.Under visible light irra-diation,in the presence of photosensitizer and electron acceptor,the Co complex catalyzes O2 evolution with a turnover frequency(TOF)of 1.0 mol(O_(2))·mol(Co)^(-1)·s^(-1)and a turnover number(TON)of 55 mol(O_(2))·mol(Co)^(-1)in pH 8 borate buffer.

Engineering of a Promoter Repressed by a Light-Regulated Transcription Factor in Escherichia coli

Light-regulated gene expression systems allow controlling gene expression in space and time with high accuracy.Contrary to previous synthetic light sensors that incorporate two-component systems which require localization at the plasma membrane,soluble one-component repression systems provide several advantageous characteristics.Firstly,they are soluble and able to diffuse across the cytoplasm.Secondly,they are smaller and of lower complexity,enabling less taxing expression and optimization of fewer parts.Thirdly,repression through steric hindrance is a widespread regulation mechanism that does not require specific interaction with host factors,potentially enabling implementation in different organisms.Herein,we present the design of the synthetic promoter P_(EL)that in combination with the light-regulated dimer EL222 constitutes a onecomponent repression system.Inspired by previously engineered synthetic promoters and the Escherichia coli lacZYA promoter,we designed P_(EL)with two EL222 operators positioned to hinder RNA polymerase binding when EL222 is bound.P_(EL)is repressed by EL222 under conditions of white light with a light-regulated repression ratio of five.Further,alternating conditions of darkness and light in cycles as short as one hour showed that repression is reversible.The design of the P_(EL)EL222 system herein presented could aid the design and implementation of analogous one-component optogenetic repression systems.Finally,we compare the P_(EL)-EL222 system with similar systems and suggest general improvements that could optimize and extend the functionality of EL222-based as well as other one-component repression systems.

Ion Coordination and Transport in Magnesium Polymer Electrolytes Based on Polyester-co-Polycarbonate

Magnesium-ion-conducting solid polymer electrolytes have been studied for rechargeable Mg metal batteries,one of the beyond-Li-ion systems.In this paper,magnesium polymer electrolytes with magnesium bis(trifluoromethane)sulfonimide(Mg(TFSI)2)salt in poly(ε-caprolactone-co-trimethylene carbonate)(PCL-PTMC)were investigated and compared with the poly(ethylene oxide)(PEO)analogs.Both thermal properties and vibrational spectroscopy indicated that the total ion conduction in the PEO electrolytes was dominated by the anion conduction due to strong polymer coordination with fully dissociated Mg2+.On the other hand,in PCL-PTMC electrolytes,there is relatively weaker polymer–cation coordination and increased anion–cation coordination.Sporadic Mg-and F-rich particles were observed on the Cu electrodes after polarization tests in Cu|Mg cells with PCL-PTMC electrolyte,suggesting that Mg was conducted in the ion complex form(MgxTFSIy)to the copper working electrode to be reduced which resulted in anion decomposition.However,the Mg metal deposition/stripping was not favorable with either Mg(TFSI)2 in PCL-PTMC or Mg(TFSI)2 in PEO,which inhibited quantitative analysis of magnesium conduction.A remaining challenge is thus to accurately assess transport numbers in these systems.