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Calcium ion batteries (CIBs) are a promising energy storage device due to the low redox potential of the Ca metal and the abundant reserves of the Ca element. However, the large radius and divalent nature of Ca2+lead to its slow ion diffusion kinetics and the lack of suitable electrode materials for Ca storage. Here, a layered structure of Na2Ti3O7(NTO) is presented as an anode material for nonaqueous CIBs. This NTO anode demonstrates a high discharge capacity of 165 mA h g–1at 100 mA g–1and a remarkable capacity retention rate of 80%, even after 2000 cycles at 500 mA g–1, surpassing the performance of all reported intercalation-type anode materials for CIBs. The NTO transfers to layered CaVIINaIXTi3O7(CNTO) with intercalation of Ca2+and extraction of Na+during the first discharge process. Then, the CNTO undergoes the reversible insertion/extraction of Ca2+during subsequent cycling. Additionally, density functional theory calculations reveal that NTO possesses a rapid two-dimensional diffusion pathway for Ca2+. Moreover, the full CIBs based on NTO as the anode further underscore its potential for CIBs. This work presents promising anode materials for CIBs, offering opportunities to promote the development of high-performance CIBs.

Low-overpotential layered hydroxides (LDHs) with high theoretical capacity are promising electrodes for supercapaterry and oxygen evolution reaction; however, the low electronic conductivity and insufficient active sites of bulk LDHs increase the internal resistance and reduce the capacity and oxygen-production efficiency of electrodes. Herein, we prepared a polyaniline-coated NiCo-layered double hydroxide intercalated with MoO42−(M-LDH@PANI) composite electrode using a two-step method. As the amount of MoO42−in the LDH increases, acicular microspheres steadily evolve into flaky microspheres with a high surface area, providing more active electrochemical sites. Moreover, the amorphous PANI coating of M-LDH boosts the electronic conductivity of the composite electrode. Accordingly, the M-LDH@PANI at an appropriate level of MoO42−exhibits significantly enhanced energy storage and catalytic performance. Experimental analyses and theoretical calculations reveal that a small amount of MoO42−is conducive to the expansion of LDH interlayer spacing, while an excessive amount of MoO42−combines with the H atoms of LDH, thus competing with OH−, resulting in reduced electrochemical performance. Moreover, M-LDH flaky microspheres can efficiently modulate deprotonation energy, greatly accelerating surface redox reactions. This study provides an explanation for an unconventional mechanism, and a method for the modification of LDH-based materials for anion intercalation.

The CeO2/g-C3N4hybrid is a kind of efficient photocatalyst with both photoinduced oxidation and reduction capability, which is of great concern in solar energy application. Herein, we reported a facile method for the synthesis of the CeO2/g-C3N4hybrid with enhanced CO2reduction and ciprofloxacin degradation performance using surface carboxylated g-C3N4(C-g-C3N4) as the substrate. The characterization results demonstrated the abundant oxygen-containing groups of C-g-C3N4in the CeO2/C-g-C3N4hybrid can effectively improve the dispersion of CeO2nanoparticles and enhance the interfacial bonding with the C-g-C3N4substrate. Density functional theory (DFT) calculations showed that a built-in electric field was formed in the CeO2/C-g-C3N4heterojunction, which can greatly improve the charge separation and transfer efficiency. Consequently, the yield of CO and the ciprofloxacin degradation efficiency have been remarkably improved. The maximum CO yield through CO2photoreduction over 3%CeO2/C-g-C3N4was 9.083, 3.922, and 2.868 times higher than that of pure CeO2, C-g-C3N4and 3%CeO2/g-C3N4bulk, respectively. The 3%CeO2/C-g-C3N4heterojunction also showed excellent photoinduced oxidation activity for ciprofloxacin degradation with a 73% degradation efficiency in 2 h, which was 1.89 and 2.76 times higher than that of pure CeO2and C-g-C3N4, respectively. Furthermore, a good photostability for a five cycle test of CO2reduction was observed over the 3%CeO2/C-g-C3N4hybrid. The possible photocatalytic mechanism was investigated by theoretical calculations and capture experiments to further understand the charge transfer behavior over the CeO2/C-g-C3N4heterojunction for CO2reduction and pollutant degradation.

Aqueous rechargeable zinc-ion batteries (AZIBs) are in a period of vigorous development due to their unparalleled advantages, including low cost, high safety and environmentally friendly etc. However, the structural damage, dissolution, low conductivity of electrode materials and slow diffusion kinetics of Zn2+ions carriers significantly limit the development of AZIBs. Herein, for the first time, we propose a general strategy for constructing multifunctional intramolecular hydrogen bond network through N-H∙∙∙O (NH4+) and O-H∙∙∙O (H2O) bonds while suppressing material dissolution (V, Mn species), enhancing the stability of layered structures, and accelerating the rapid diffusion of protons. To better reveal the hydrogen bond and enhanced proton transport, a range of in/ex-situcharacterization techniques in conjunction with DFT calculations have been implemented. As a proof of concept, this strategy has proven to be universally applicable, with both vanadium oxide (400.6 Wh kg−1/6489.3 W kg−1, 85% over 4000 cycles) and manganese oxide (433.6 Wh kg−1/2972.8 W kg−1, 100% after 500 cycles) achieving significant electrochemical performance improvements, particularly in terms of rate performance and cycle performance, which are better than most comparable materials. The insights obtained in this study have deepened the understanding based on the hydrogen bond in AZIBs and also brought new opportunities for improving the energy density of other types of aqueous batteries in the future.