Electrochemical exfoliation of ultrathin ternary molybdenum sulfoselenide nanosheets to boost the energy-efficient hydrogen evolution reaction

Investigation of seawater electrolyte on hydrogen evolution reaction from the perspective of kinetics and energy consumption using an Ni-based electrocatalyst supported on carbon nanotubes

In this study, a Ni-based composite incorporating Ni4N and La2O3 supported on carbon nanotubes (Ni-La-Ni4N/CNT) was synthesized as an efficiency electrocatalyst towards the hydrogen evolution reaction in different electrolytes with the kinetics and energy consumption investigated in detail. The Ni-La-Ni4N/CNT exhibits overpotentials of 124 mV and 200 mV at the current density of 10 mA cm-2 in 1.0 M KOH and alkaline seawater, respectively. As quantitative comparison, the exchange current density (j°) based on Volmer-Heyrovsky-Tafel mechanism was calculated from various polarization curves, which indicated that the addition of NaCl in alkaline medium or using seawater alone reduced the reactivity of the catalyst. The activity of Ni-La-Ni4N/CNT in alkaline seawater was equal to 91% of that in 1.0 M KOH. Furthermore, dynamic polarization resistance and corresponding current were obtained by the analysis of the equivalent circuit model with the extended Kalman filter algorithm. The analysis of the resistance power at 1 mW also shows that the current between the conditions in KOH and in seawater is 2.76 times. Adding alkaline substances to seawater can narrow it to 1.19 times. These strategies provide novel approaches for inspecting the activity changes of materials in different electrochemical environments.

Aqueous Rechargeable Zn-N2 Battery Assembled by Bifunctional Cobalt Phosphate Nanocrystals-Loaded Carbon Nanosheets for Simultaneous NH3 Production and Power Generation

Developing cost-effective and controllable technologies beyond traditional overall N₂ electrocatalysis is critical for the large-scale production of NH₃ through electrochemical N₂ reduction reaction (NRR) under ambient conditions. Herein, the aqueous rechargeable Zn-N₂ battery, assembled by coupling the bifunctional cobalt phosphate nanocrystals-loaded heteroatoms-doped carbon nanosheets (CoPi/NPCS) as cathode electrocatalyst and the commercial Zn plate as anode with KOH electrolyte, was fabricated for the sustainable reduction of N₂ to NH₃ and power generation during discharge process. Benefiting from the desirable active components of cobalt phosphate nanocrystals and the synergistic effect between nanocrystals and carbon substrates, the CoPi/NPCS catalyst exhibits the enhanced NRR and oxygen evolution reaction (OER) performance in alkaline electrolyte. And the cobalt phosphates are confirmed as active components through the associative pathway toward NRR. When measured in the flow battery configuration with gas diffusion electrode by flowing N₂ during discharge, this CoPi/NPCS-catalyzed Zn-N₂ battery enables the high N₂-to-NH₃ yield rate of 14.7 μg h^-1 mg_cat.^-1 and Faradaic efficiency of 16.35% at 0.6 V vs Zn²⁺/Zn, which can be able to maintain stable in discharge processes during cycling tests. Moreover, the impressive power output of the peak power density of 0.49 mW cm^-2 and the energy density of 147.6 mWh g_zn^-1 are still achieved by this Zn-N₂ battery, which are both higher than those of previously reported Zn-N₂ batteries. This work not only provides the guideline for the rational design of robust and active bifunctional NRR-OER catalysts but also develops a reasonable and promising technology for efficient electrochemical N₂-to-NH₃ and power generation.

Nanoconfined Tin Oxide within N-Doped Nanocarbon Supported on Electrochemically Exfoliated Graphene for Efficient Electroreduction of CO2 to Formate and C1 Products

Developing low-cost and effective electrocatalysts for electrochemical reduction of CO₂ (CO₂ER) is critical to CO₂ conversion and utilization. Herein, we report a novel two-dimensional (2D) confined electrocatalyst composed of core-shell structured tin oxide nanoparticles (NPs) encapsulated into N-doped carbon (NC) supported on electrochemically exfoliated graphene (SnO₂⊃NC@EEG) prepared by in situ carbonization of a 2-methylimidazole/SnO₂ complex@poly(vinyl pyrrolidone) (PVP)-modified EEG precursor. The SnO₂ NPs with an average size of ∼10 nm are confined in the NC shells with a thickness of 0.7 nm derived from 2-methylimidazole. The resulting 2D confined electrocatalyst significantly enhances the CO₂ER performance with a small onset potential of -0.45 V, and high Faradic efficiencies of 81.2 and 93.2% for HCOO^- and C1 products at -1.2 V, respectively, which is far superior to other reported SnO₂/carbon-based CO₂ER hybrids. The superb CO₂ER catalytic activity of the SnO₂⊃NC@EEG has resulted from the positive effect of N dopants and a strong confinement effect, which significantly expedites the CO₂ adsorption associated with charge transfer from the NC to SnO₂ NPs during CO₂ER electrocatalysis.