The microscopic structure of dimethyl sulfoxide (DMSO) aqueous solutions was investigated by Fourier transform infrared (FTIR) spectroscopy and ultrafast IR spectroscopy. The structural dynamics of the binary mixtures were reflected by using thiocyanate anion (SCN–) as a local vibrational probe. FTIR spectra of SCN– anion showed that the hydrogen bond networks of water are affected by the presence of DMSO molecules, and the peak position and bandwidth of SCN– anions are red shifted and narrowed accordingly because of the weak hydration in the binary mixture. The vibrational lifetime of the SCN– anion showed almost linear enhancement with the increase of DMSO, which can be explained by the weak interaction between SCN– and the hydrophobic groups in the DMSO molecule. However, the rotational dynamics of SCN– are slowing down significantly and showed a maximum response at X DMSO (mole fraction) of 0.35, which is mainly caused by the confinement of SCN– anions positioned in the vicinity of the complex structure formed between DMSO and water molecules. The concentration-dependent rotational dynamics of water molecules and SCN– anions are having similar behavior, indicating that the complex structure can be formed between water and DMSO molecules because of the strong interaction. The result also demonstrates that the structural inhomogeneity in aqueous solution can be unraveled by monitoring the vibrational relaxation dynamics of SCN– anion serving as the local vibrational probe.

“Water-in-salt” electrolytes have been demonstrated to have potential applications in the field of high-voltage aqueous lithium ion batteries (LIBs). However, the basic understanding of the structure and dynamics of the concentrated “water-in-salt” electrolytes at the molecular level is still lacking. In this report, the structural dynamics of the concentrated lithium bis­(tri­fluoro­methane sulfonyl)­imide (LiTFSI) aqueous solutions were investigated using Fourier transform infrared (FTIR) spectroscopy and ultrafast IR spectroscopy. The OD stretches of the water molecule and the thiocyanate (SCN–) anionic solute were utilized as the IR probes to monitor the local structure of the concentrated LiTFSI aqueous solutions. The concentration-dependent IR spectra and vibrational relaxation dynamics of the SCN– anion were systematically measured and analyzed. It was found that the vibrational population of the SCN– anion decayed at a much faster rate as the LiTFSI bulk concentration increased. From the static IR spectra and vibrational relaxation dynamics of SCN–, it was firmly confirmed that the SCN– anion interacted with the Li+ cations surrounded with domains of bulk-like water in the concentrated LiTFSI aqueous solutions. The rotational dynamics and spectral diffusion measurements of the SCN– anion further showed that the rotation of the SCN– anionic probe is strongly confined and restricted by the specific network structure formed by a framework of the TFSI– anions and the associated interfacial water molecules. Macroscopic conductivity and viscosity measurements were also performed for the LiTFSI aqueous solutions in order to elucidate a full picture of the liquid structure. The rotational dynamics of the SCN– anion decoupled from the viscosity of the solution are suggested to be segregated from the dynamics of the heterogeneous domains formed by the extended ion network of the TFSI– anions. All of these results demonstrated that the structural dynamics of the concentrated LiTFSI aqueous solutions can be revealed from the viewpoint of the anionic solute. And the heterogeneous structures in the LiTFSI solutions proposed by the molecular dynamic (MD) simulation were supported by experiment. The results in this work are expected to provide a basic understanding of the microscopic structure and transport mechanism of lithium ions in the water-in-salt electrolytes of LIBs.

Vibrational relaxation and the rotational dynamics of water molecules encapsulated in reverse micelles (RMs) have been investigated by ultrafast infrared (IR) spectroscopy and two-dimensional IR (2D IR) spectroscopy. By changing the counterion of the hydrophilic headgroup in the RMs formed by Aerosol-OT (AOT) from Na+ to K+, Cs+ and Ca2+, we could determine the specific counterion effects on the rotational dynamics of water molecules. The orientational relaxation time constant of water decreases in the order Ca2+ > Na+ > K+ > Cs+. The SCN– anionic probe and counterion can form ion pairs at the interfacial region of the RMs. The rotational dynamics of SCN– anion significantly decreases because of the synergistic effects of confinement and the surface interactions in the interfacial region of the RMs. The results can provide a new understanding of the cationic Hofmeister effect at the molecular level observed in biological studies.

Ac obaltc orrole ……w an appended crown ether unit displays significantly boosted electrocatalytic hydrogen evolution activity in the presence of water as reported by Rui Cao and coworkers in their Communication (e202114310). Thec rown ether unit is able to grab water molecules through hydrogen bond interactions.T he established water network can play critical roles in assisting proton transfer, leading to improved electrocatalytic activity for the hydrogen evolution reaction, which mimics water-network-assisted proton transfer as found in metalloproteins.

The mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]­BF4) ionic liquids (ILs) and water as a function of IL concentrations have been investigated by Fourier transform infrared (FTIR) spectroscopy and ultrafast two-dimensional IR (2D IR) spectroscopy. FTIR spectra of the mixtures resolve two different types of water species, one interacting with the BF4 – anions and the other associated with bulklike water molecules. These two water species are in a dynamic equilibrium through forming different hydrogen bonding configurations which are separated by more than 100 cm–1 in the IR spectra. The structural dynamics of the IL mixtures are further revealed by monitoring the vibrational relaxation dynamics of the OD stretching group of interfacial water molecules hydrogen bonded to BF4 – anions. With the increase of the IL bulk concentration, vibrational population and rotational dynamics of the interfacial water molecules can be described by a biexponential decay function and are strongly dependent on the IL concentrations. Furthermore, the ultrafast hydrogen bond exchanging between water and BF4 – anions in the ILs are also measured using 2D IR spectroscopy. The average hydrogen bond exchanging rate is determined to be 19 ± 4 ps, which is around 3 times slower than that in the NaBF4 electrolyte aqueous solution. The much slower hydrogen bond exchanging rate indicates that the local structure of ILs and water molecules are strongly mediated by the steric effect of the cationic group in the ILs, which is proposed to be responsible for the formation of the heterogeneous structure in the IL mixtures. By using SCN– as the anionic probe, the structural inhomogeneity in the IL solutions can be confirmed from the distinct rotational dynamics of the SCN–, which is segregated from the rotational dynamics of water molecules in the IL mixtures.

The development of multifunctional non-precious transition metal electrocatalysts is technologically significant in hydrogen and oxygen electrochemistry but challenging. Here we exploit interface engineering to construct a novel interface catalyst of Ni3N and Co2N that exhibits multifunctional hydrogen and oxygen electrochemical activities in alkaline media. The interface catalysts of Ni3N/Co2N show superior bifunctional activity for hydrogen electrochemistry comparable to the state-of-the-art Pt catalyst, as well as high oxygen evolution reaction activity. Furthermore, the multifunctional Ni3N/Co2N interface electrocatalysts demonstrate excellent applications in water splitting for H2 generation and a highly stable Swagelok-type Ni–H battery for H2 utilization. Density functional theory calculations further confirm that the interfacial charge transfer from Ni to Co and N in Ni3N/Co2N efficiently enhances the dissociative adsorption of H2 and optimizes the adsorption configurations and binding energies of the intermediate hydrogen and hydroxide in the multifunctional reactions.

The development of active, durable, and nonprecious electrocatalysts for hydrogen electrochemistry is highly desirable but challenging. In this work, we design and fabricate a novel interface catalyst of Ni and Co 2 N (Ni/Co 2 N) for hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR). The Ni/Co 2 N interfacial catalysts not only achieve a current density of −10.0 mA cm −2 with an overpotential of 16.2 mV for HER but also provide a HOR current density of 2.35 mA cm −2 at 0.1 V vs reversible hydrogen electrode (RHE). Furthermore, the electrode couple made of the Ni/ Co 2 N interfacial catalysts requires only a cell voltage of 1.57 V to gain a current density of 10 mA cm −2 for overall water splitting. Hybridizations in the three elements of Ni-3d, N-2p, and Co-3d result in charge transfer in the interfacial junction of the Ni and Co 2 N materials. Our density functional theory calculations show that both the interfacial N and Co sites of Ni/Co 2 N prefer to hydrogen adsorption in the hydrogen catalytic activities. This study provides a new approach for the construction of multifunctional catalysts for hydrogen electrochemistry.

Proton transfer is vital for many biological and chemical reactions. Hydrogen‐bonded water‐containing networks are often found in enzymes to assist proton transfer, but similar strategy has been rarely presented by synthetic catalysts. We herein report the Co corrole 1 with an appended crown ether unit and its boosted activity for the hydrogen evolution reaction (HER). Crystallographic and 1H NMR studies proved that the crown ether of 1 can grab water via hydrogen bonds. By using protic acids as proton sources, the HER activity of 1 was largely boosted with added water, while the activity of crown‐ether‐free analogues showed very small enhancement. Inhibition studies by adding 1) external 18‐crown‐6‐ether to extract water molecules and 2) potassium ion or N‐benzyl‐n‐butylamine to block the crown ether of 1 further confirmed its critical role in assisting proton transfer via grabbed water molecules. This work presents a synthetic example to boost HER through water‐containing networks.