A Coupled System of Ni3S2 and Rh Complex with Biomimetic Function for Electrocatalytic 1,4-NAD(P)H Regeneration.

NAD(P)H cofactor is a critical energy and electron carrier in biocatalysis and photosynthesis, but the artificial reduction of NAD(P)+ to regenerate bioactive 1,4-NAD(P)H with both high activity and selectivity is challenging. Herein, we found that a coupled system of a Ni3S2 electrode and a Rh complex in an electrolyte (denoted as Ni3S2-Rh) can catalyze the reduction of NAD(P)+ to 1,4-NAD(P)H with superior activity and selectivity. The optimized selectivity in 1,4-NADH can be up to 99.1%, much higher than that for Ni3S2 (80%); the normalized activity of Ni3S2-Rh is about 5.8 times that of Ni3S2 and 13.2 times that of the Rh complex. The high performance of Ni3S2-Rh is attributed to the synergistic effect between metal sulfides and Rh complex. The NAD+ reduction reaction proceeds via a concerted electron-proton transfer (CEPT) mechanism in the Ni3S2-Rh system, in which Ni3S2 acts as a proton and electron-transfer mediator to accelerate the formation of Rh hydride (Rh-H), and then the Rh-H regioselectively transfers the hydride to NAD+ to form 1,4-NADH. The artificial system Ni3S2-Rh essentially mimics the functions of ferredoxin-NADP+ reductase in nature.

Electrosynthesis of H2O2 Promoted by π-π Interaction on a Metal-Free Carbon Catalyst.

The synthesis of hydrogen peroxide (H2O2) through electrocatalytic oxygen reduction reaction is an ideal alternative to the current energy-intensive anthraquinone process, but developing cost-effective and high-efficiency electrocatalysts is still challenging. Herein, a metal-free graphitic carbon nitride/carbon nanotube (g-C3N4/CNT) hybrid catalyst can enhance H2O2 production via π-π interaction is reported, achieving almost unity (97%) H2O2 production at 0.57 V with high selectivity of over 92% across the wide potential range from 0.6 to 0 V. Other carbon materials with weak interaction with g-C3N4, such as acetylene black and super P, show markedly weakened H2O2 production, indicating the importance of π-π interaction. Electron transfer kinetic analysis combined with density functional theory calculations indicates that the synergistic effect between g-C3N4 and CNT enhances electron transfer and O2 activation between g-C3N4 and CNT, leading to enhanced H2O2 production performance. This work provides a complementary approach for H2O2 production from oxygen reduction besides introducing oxygenated groups or heteroatom doping into carbon materials.

Extremely Active and Robust Ir-Mn Dual-Atom Electrocatalyst for Oxygen Evolution Reaction by Oxygen-Oxygen Radical Coupling Mechanism.

A novel Ir-Mn dual-atom electrocatalyst is synthesized by a facile ion-exchange method by incorporating Ir in SrMnO3, which yields an extremely high activity and stability for the oxygen evolution reaction (OER). The ion exchange process occurs in a self-limitation way, which favors the formation of Ir-Mn dual-atom in the IrMnO9 unit. The incorporation of Ir modulates the electronic structure of both Ir and Mn, thereby resulting in a shorter distance of the Ir-Mn dual-atom (2.41 Å) than the Mn-Mn dual-atom (2.49 Å). The modulated Ir-Mn dual-atom enables the same spin direction O (↑) of the adsorbed *O intermediates, thus facilitating the direct coupling of the two adsorbed *O intermediates to release O2 via the oxygen-oxygen radical coupling mechanism. Electrochemical tests reveal that the Ir-SrMnO3 exhibits a superior OER's activity with a low overpotential of 207 mV at 10 mA cm-2 and achieves a mass specific activity of 1100 A gIr-1 at 1.5 V. The proton-exchange-membrane water electrolyzer with the Ir-SrMnO3 catalyst exhibits a low electrolysis voltage of 1.63 V at 1.0 A cm-2 and a stable 2000-h operation with a decay of only 15 µV h-1 at 0.5 A cm-2.

Zinc-Mediated Template Synthesis of Hierarchical Porous N-Doped Carbon Electrocatalysts for Efficient Oxygen Reduction.

The development of highly active and low-cost catalysts for use in oxygen reduction reaction (ORR) is crucial to many advanced and eco-friendly energy techniques. N-doped carbons are promising ORR catalysts. However, their performance is still limited. In this work, a zinc-mediated template synthesis strategy for the development of a highly active ORR catalyst with hierarchical porous structures was presented. The optimal catalyst exhibited high ORR performance in a 0.1 M KOH solution, with a half-wave potential of 0.89 V vs. RHE. Additionally, the catalyst exhibited excellent methanol tolerance and stability. After a 20,000 s continuous operation, no obvious performance decay was observed. When used as the air-electrode catalyst in a zinc-air battery (ZAB), it delivered an outstanding discharging performance, with peak power density and specific capacity as high as 196.3 mW cm-2 and 811.5 mAh gZn-1, respectively. Its high performance and stability endow it with potential in practical and commercial applications as a highly active ORR catalyst. Additionally, it is believed that the presented strategy can be applied to the rational design and fabrication of highly active and stable ORR catalysts for use in eco-friendly and future-oriented energy techniques.

Rationally Modulating the Functions of Ni3 Sn2 -NiSnOx Nanocomposite Electrocatalysts towards Enhanced Hydrogen Evolution Reaction.

Identifying electrocatalysts with functions of easy dissociation of water, rapid transformation of hydroxyl and facile hydrogen-hydrogen bond formation are indispensable while challenge for realizing efficient alkaline hydrogen evolution reaction (HER). Herein, we presented the design of Ni3 Sn2 -NiSnOx nanocomposites towards addressing this challenge. We showed that Ni3 Sn2 possessed ideal hydrogen adsorption and low hydroxyl adsorption abilities and NiSnOx facilitated water dissociation and hydroxyl transfer process, respectively. Consequently, the fine-tuned interplay of the two functional parts realized the mutual coordination among the multiple functions and led to significantly boosted HER kinetics. Current densities of 10 and 1000 mA cm-2 were obtained at overpotentials of 14 and 165 mV on the optimized catalyst. This work highlights the significance of considering intrinsic interactions between active sites and all pertinent intermediates on obtaining promising electrocatalysts.

Boosting Electrochemical Water Oxidation on NiFe (oxy) Hydroxides by Constructing Schottky Junction toward Water Electrolysis under Industrial Conditions.

The practical deployment of promising NiFe-based oxygen evolution reaction (OER) electrocatalysts is heavily limited due to the constrain in both stability and activity under industrial conditions. Herein, a 3D free-standing NiFe(oxy)hydroxide-based electrode with Schottky junction is constructed, in which NiFe(oxy)hydroxide (NiFe(OH)x ) nanosheets are chemically assembled on the top of metal-like Ni3 S2 scaffold that are in situ formed on commercial Ni mesh. Such an assembly enhances the binding strength of each components, promotes the charge transfer across the interfaces, and modulates the electronic and nanostructural features of NiFe(OH)x . Consequently, the electrode delivers current densities of as high as 500 and 1000 mA cm-2 for OER at overpotentials of only 248 and 270 mV with long-term stability in 1 m KOH. When it was paired with a NiMo hydrogen evolution cathode in a practical two-electrode system, a current density of 1000 mA cm-2 is achieved at a low cell voltage of ≈1.61 V at 80 °C in 30% KOH without losing performance for at least 1500 h. This is the best performance reported thus far for alkaline water electrolysis under industrial conditions, demonstrating its great potential for practical applications.

Water-participated mild oxidation of ethane to acetaldehyde.

The direct conversion of low alkane such as ethane into high-value-added chemicals has remained a great challenge since the development of natural gas utilization. Herein, we achieve an efficient one-step conversion of ethane to C2 oxygenates on a Rh1/AC-SNI catalyst under a mild condition, which delivers a turnover frequency as high as 158.5 h-1. 18O isotope-GC-MS shows that the formation of ethanol and acetaldehyde follows two distinct pathways, where oxygen and water directly participate in the formation of ethanol and acetaldehyde, respectively. In situ formed intermediate species of oxygen radicals, hydroxyl radicals, vinyl groups, and ethyl groups are captured by laser desorption ionization/time of flight mass spectrometer. Density functional theory calculation shows that the activation barrier of the rate-determining step for acetaldehyde formation is much lower than that of ethanol, leading to the higher selectivity of acetaldehyde in all the products.

Hydrogen Evolution Reaction on Single-Atom Pt Doped in Ni Matrix under Strong Alkaline Condition.

Pt catalyst has been considered as the state-of-the-art catalyst for hydrogen evolution reaction (HER) under acid condition. However, its catalytic kinetics under alkaline conditions is not well-understood. Herein, we report a Ni-Pt(SAs) (SAs = single atoms) catalyst with Pt atomically dispersed in a Ni matrix, and it possesses an impressive HER performance with an overpotential as low as 210 mV at 500 mA cm-2 in strong alkaline electrolyte (7 M KOH), which is much higher than Pt nanoparticle-modified Ni catalyst (Ni-Pt(NPs)). Kinetics analysis reveals that Pt doping in the Ni matrix can accelerate the Volmer step on the Ni-Pt surface. Moreover, Ni-Pt(SAs) displays a more favorable kinetics for H2 formation reaction at high current density than Ni-Pt(NPs). Theoretical calculations reveal that atomically dispersed Pt weakens the adsorption of both H and OH on the surface of Ni-Pt electrode and promotes H2 formation from surface H on Ni-Pt(SAs).