A bicomponent synergistic MoxW1-xS2/aluminum nitride vdW heterojunction for enhanced photocatalytic hydrogen evolution: a first principles study.

The coupling of two-dimensional van der Waals heterojunctions is an effective way to achieve photocatalytic hydrogen production. This paper designs the MoxW1-xS2/AlN (x = 0, 0.25, 0.5, 0.75, 1) van der Waals heterojunction as a possible photocatalytic material. By using first-principles calculations, the effects of different Mo/W ratios on the band gap and photocatalytic hydrogen production performance of heterojunctions were investigated. The results show that the heterojunction is a direct Z-scheme photocatalyst and can achieve overall water splitting. By calculating the absorption spectrum, it is found that the heterojunction has a wider visible light absorption range when the bimetal is added, and there is still a strong absorption peak at 615 nm. With the increase of the Mo atom ratio, the absorption spectrum is red-shifted. The Gibbs free energy of the two-component Mo0.5W0.5S2/AlN heterojunction is only -0.028 eV. Our work provides a new perspective for the modification of 2D transition metal dichalcogenide photocatalytic heterojunctions.

Two-dimensional AlN/g-CNs van der Waals type-II heterojunction for water splitting.

A type-II van der Waals heterojunction photocatalyst is not only an ideal material for hydrogen production by water splitting, but also an important way to improve efficiency and produce low-cost clean energy. In this work, we unexpectedly found that monolayers of AlN and C2N, g-C3N4, and C6N8 all formed type-II heterojunctions according to density functional theory, and we report a comparison of their photocatalytic performance. Among them, the AlN/C2N heterojunction has an appropriate band gap value of 1.61 eV for visible light water splitting. It has higher carrier mobility than the AlN/g-C3N4 heterojunction (electron 253.1 cm2 V-1 s-1 > 31.6 cm2 V-1 s-1 and hole 11043.4 cm2 V-1 s-1 > 524.7 cm2 V-1 s-1), and an absorption peak similar those of monolayer C2N in visible light (8 × 104 cm-1) and monolayer AlN in ultraviolet light (11 × 104 cm-1). The Bader charge shows that the charge transfer number of the AlN/g-C3N4 heterojunction is higher than that of the AlN/C2N heterojunction, and its Gibbs free energy (-0.22 eV) is smaller than that of single-layer g-C3N4 (-0.30 eV). The AlN/C6N8 heterojunction also has a perfect band gap of 2.16 eV and an absorption peak of over 10 × 104 cm-1 in the UV region. Since a type-II heterojunction can effectively promote the separation of photogenerated electron-hole pairs and prevent their rapid recombination, the above heterojunctions are promising candidates for new photocatalysts.

Synergistic Fe-Se Atom Pairs as Bifunctional Oxygen Electrocatalysts Boost Low-Temperature Rechargeable Zn-Air Battery.

Herein, we successfully construct bifunctional electrocatalysts by synthesizing atomically dispersed Fe-Se atom pairs supported on N-doped carbon (Fe-Se/NC). The obtained Fe-Se/NC shows a noteworthy bifunctional oxygen catalytic performance with a low potential difference of 0.698 V, far superior to that of reported Fe-based single-atom catalysts. The theoretical calculations reveal that p-d orbital hybridization around the Fe-Se atom pairs leads to remarkably asymmetrical polarized charge distributions. Fe-Se/NC based solid-state rechargeable Zn-air batteries (ZABs-Fe-Se/NC) present stable charge/discharge of 200 h (1090 cycles) at 20 mA cm-2 at 25 °C, which is 6.9 times of ZABs-Pt/C+Ir/C. At extremely low temperature of -40 °C, ZABs-Fe-Se/NC displays an ultra-robust cycling performance of 741 h (4041 cycles) at 1 mA cm-2 , which is about 11.7 times of ZABs-Pt/C+Ir/C. More importantly, ZABs-Fe-Se/NC could be operated for 133 h (725 cycles) even at 5 mA cm-2 at -40 °C.

Edge-Hosted Mn-N4-C12 Site Tunes Adsorption Energy for Ultralow-Temperature and High-Capacity Solid-State Zn-Air Battery.

Robust operation of Zn-air batteries (ZABs) with high capacity and excellent energy efficiency is desirable for practical harsh applications, whose bottlenecks are mainly originated from the sluggish oxygen catalytic kinetics and unstable Zn|electrolyte interface. In this work, we synthesized the edge-hosted Mn-N4-C12 coordination supported on N-doped defective carbon (Mn1/NDC) catalyst, exhibiting a good bifunctional performance of the oxygen reduction/evolution reaction (ORR/OER) with a low potential gap of 0.684 V. Theoretical calculation reveals that the edge-hosted Mn-N4-C12 coordination displayed the lowest overpotential of the ORR/OER owing to the decreased adsorption free energy of OH*. The Mn1/NDC-based aqueous ZABs deliver impressive rate performance, ultralong discharging lifespan, and excellent stability. Notably, the assembled solid-state ZABs demonstrate a high capacity of 1.29 Ah, a large critical current density of 8 mA cm-2, and robust cycling stability with excellent energy efficiency at -40 °C, which should be attributed to the good bifunctional performance of Mn1/NDC and anti-freezing solid-state electrolyte (SSE). Meanwhile, the zincophilic nanocomposite SSE with high polarity accounts for the stable Zn|SSE interface compatibility. This work not only highlights the importance of the atomic structure design of oxygen electrocatalysts for ultralow-temperature and high-capacity ZABs but also spurs the development of sustainable Zn-based batteries at harsh conditions.

Quasi-solid-state Zn-air batteries with an atomically dispersed cobalt electrocatalyst and organohydrogel electrolyte.

Quasi-solid-state Zn-air batteries are usually limited to relatively low-rate ability (<10 mA cm-2), which is caused in part by sluggish oxygen electrocatalysis and unstable electrochemical interfaces. Here we present a high-rate and robust quasi-solid-state Zn-air battery enabled by atomically dispersed cobalt sites anchored on wrinkled nitrogen doped graphene as the air cathode and a polyacrylamide organohydrogel electrolyte with its hydrogen-bond network modified by the addition of dimethyl sulfoxide. This design enables a cycling current density of 100 mA cm-2 over 50 h at 25 °C. A low-temperature cycling stability of over 300 h (at 0.5 mA cm-2) with over 90% capacity retention at -60 °C and a broad temperature adaptability (-60 to 60 °C) are also demonstrated.

Bismuth with abundant defects for electrocatalytic CO2 reduction and Zn-CO2 batteries.

To regulate the electronic structure of Bi sites and enhance their intrinsic activity, metal Bi with abundant defects was constructed. The optimized sample displayed a higher selectivity (93.9% at -0.9 V) and a larger current density (-10 mA cm-2 at -1.0 V) towards electrocatalytic CO2 reduction to formate, which can be mainly attributed to abundant defect sites and the optimized electronic structure. The assembled Zn-CO2 batteries displayed a power density of 1.16 mW cm-2 and a cycling stability up to 22 h. This work deepens the research of Bi-based catalysts towards CO2 transformation and related energy devices.