Mechanistic insights into higher alcohol synthesis from syngas on Rh/Cu single-atom alloy catalysts.

Low cost Cu-based catalysts are attractive options in catalyzing higher alcohol synthesis (HAS) from syngas. Introducing isolated Rh single atoms into the surfaces of these Cu catalysts has the potential to dramatically improve the performance of these Cu-based catalysts. In this work, extensive density functional theory (DFT) calculations were performed with periodic slab models to systematically investigate the possibility of using Rh/Cu single-atom alloys (SAAs) as HAS catalysts. The mechanism of ethanol synthesis from syngas on the representative Rh/Cu(111) and Rh/Cu(100) surfaces was elucidated. All possible formation pathways of the C1 and C2 fragments leading to the ethanol main product, as well as the methane and methanol by-products were considered. Our calculations show that for ethanol formation, the C-C bond coupling is easier over the Rh/Cu SAA catalysts than pure Cu catalysts, suggesting that Rh/Cu SAA catalysts are more favorable for the formation of higher alcohols.

Strategy of Voltage Match on the Maximum Power Point for a High-Efficiency Photorechargeable Device.

A photorechargeable device can generate power from sunlight and store it in one device, which has a broad application prospect in the future. However, if the working state of the photovoltaic part in the photorechargeable device deviates from the maximum power point, its actual power conversion efficiency will reduce. The strategy of voltage match on the maximum power point is reported to achieve a high overall efficiency (ηoa) of the photorechargeable device assembled by a passivated emitter and rear cell (PERC) solar cell and Ni-based asymmetric capacitors. According to matching the voltage of the maximum power point of the photovoltaic part, the charging characteristics of the energy storage part are adjusted to realize a high actual power conversion efficiency of the photovoltaic part (ηpv). The ηpv of a Ni(OH)2-rGO-based photorechargeable device is 21.53%, and the ηoa is up to 14.55%. This strategy can promote further practical application for the development of photorechargeable devices.

Battery-Type-Behavior-Retention Ni(OH)2-rGO Composite for an Ultrahigh-Specific-Capacity Asymmetric Electrochemical Capacitor Electrode.

Nanosized battery-type materials applied in electrochemical capacitors can effectively reduce a series of problems caused by low conductivity and large volume changes. However, this approach will lead to the charging and discharging process being dominated by capacitive behavior, resulting in a serious decline in the specific capacity of the material. By controlling the material particles to an appropriate size and a suitable number of nanosheet layers, the battery-type behavior can be retained to maintain a large capacity. Here, Ni(OH)2, which is a typical battery-type material, is grown on the surface of reduced graphene oxide to prepare a composite electrode. By controlling the dosage of the nickel source, the composite material with an appropriate Ni(OH)2 nanosheet size and a suitable number of layers was prepared. The high-capacity electrode material was obtained by retaining the battery-type behavior. The prepared electrode had a specific capacity of 397.22 mA h g-1 at 2 A g-1. After the current density was increased to 20 A g-1, the retention rate was as high as 84%. The prepared asymmetric electrochemical capacitor had an energy density of 30.91 W h kg-1 at a power density of 1319.86 W kg-1 and the retention rate could reach 79% after 20,000 cycles. We advocate an optimization strategy that retains the battery-type behavior of electrode materials by increasing the size of nanosheets and the number of layers, which can significantly improve the energy density while combining the advantage of the high rate capability of the electrochemical capacitor.

Ir-Doped Co(OH)2 nanosheets as an efficient electrocatalyst for the oxygen evolution reaction.

In recent years, Co-based metal-organic frameworks (Co-MOFs) have received significant research interest because of their large specific surface area, high porosity, tunable structure and topological flexibility. However, their comparatively weak electrical conductivity and inferior stability drastically restrict the application of Co-MOFs in the synthesis of electrocatalysts. In this study, ZIF-67 was grown on nickel foam by a room temperature soaking method, and then Ir-Co(OH)2@ZIF-67/NF was assembled by a hydrothermal method. The prepared Ir-Co(OH)2@ZIF-67/NF nanosheets exhibit remarkable conductivity, larger electrochemical active surface area and wider electron transport channels. Only ultralow overpotentials of 198 mV, 263 mV, and 300 mV were needed for Ir-Co(OH)2@ZIF-67/NF to reach the current densities of 10 mA cm-2, 50 mA cm-2, 100 mA cm-2, meanwhile, no obvious degradation of the current density at 10 mA cm-2 was observed for about 16 h. This work may provide a promising strategy for developing high-performance MOF-derived materials as electrocatalysts for the OER under alkaline conditions.

Spherical V-doped nickel-iron LDH decorated on Ni3S2 as a high-efficiency electrocatalyst for the oxygen evolution reaction.

Due to the slow reaction kinetics of the oxygen evolution reaction (OER), the electrolysis rate of water is greatly limited. Therefore, it is of great significance to study stable and efficient non-noble metal based electrocatalysts. In this paper, three-dimensional (3D) spherical V-NiFe LDH@Ni3S2 was developed by exquisitely decorating ultra-thin V-doped NiFe layered dihydroxide (NiFe-LDH) on Ni3S2 nanosheets supported by nickel foam (NF). It is worth mentioning that V-NiFe LDH@Ni3S2 exhibits an excellent electrocatalytic performance and only 178 mV overpotential is required in 1 M KOH to achieve a current density of 10 mA cm-2. Long-term chronoamperometry manifests its superior electrochemical stability. The combination of NiFe LDH and conductive substrate coupling can drastically afford abundant active sites and accelerate charge transfer, and V doping can markedly regulate the electronic structure. Therefore, the activity and durability of the electrocatalysts are greatly improved. This study may provide a new strategy for the preparation of efficient OER electrocatalysts.

Selenide-based 3D folded polymetallic nanosheets for a highly efficient oxygen evolution reaction.

Electrochemical water splitting, which is considered to be one of the fruitful strategies to achieve efficient and pollution-free hydrogen production, has been deemed as a key technology to achieve renewable energy conversion. Oxygen evolution reaction (OER) is a decisive step in water splitting. Slow kinetics seriously limits the effective utilization of energy thus it is extremely urgent to develop electrocatalysts that can effectively reduce the reaction energy barrier thus accelerate OER kinetics. Here, Mn-Co0.85Se/NiSe2/NF nanosheets with 3D folded structure was assembled on Ni foam by electrodeposition and vapor-deposition method. Mn-Co0.85Se/NiSe2/NF can achieve a current density of 10 mA cm-2 with only 175 mV overpotential in an alkaline environment of 1 M KOH, which is much lower than other reported catalysts. In addition, catalyst Mn-Co0.85Se/NiSe2/NF also performed well in long-term stability tests. Through the synergy of polymetallic, the improvement of catalyst surface energy together with the tuning of electronic structure and the optimization of conductivity can be realized. This work may provide a feasible strategy for the design of efficient selenide-based oxygen evolution reaction catalysts.

Direct conversion of CO2 to a jet fuel over CoFe alloy catalysts.

The direct conversion of carbon dioxide (CO2) using green hydrogen is a sustainable approach to jet fuel production. However, achieving a high level of performance remains a formidable challenge due to the inertness of CO2 and its low activity for subsequent C-C bond formation. In this study, we prepared a Na-modified CoFe alloy catalyst using layered double-hydroxide precursors that directly transforms CO2 to a jet fuel composed of C8-C16 jet-fuel-range hydrocarbons with very high selectivity. At a temperature of 240°C and pressure of 3 MPa, the catalyst achieves an unprecedentedly high C8-C16 selectivity of 63.5% with 10.2% CO2 conversion and a low combined selectivity of less than 22% toward undesired CO and CH4. Spectroscopic and computational studies show that the promotion of the coupling reaction between the carbon species and inhibition of the undesired CO2 methanation occur mainly due to the utilization of the CoFe alloy structure and addition of the Na promoter. This study provides a viable technique for the highly selective synthesis of eco-friendly and carbon-neutral jet fuel from CO2.