Dinitrogen Reduction Coupled with Methanol Oxidation for Low Overpotential Electrochemical NH3 Synthesis Over Cobalt Pyrophosphate as Bifunctional Catalyst

Hierarchical Porous Carbon Supported Co2P2O7 Nanoparticles for Oxygen Evolution and Oxygen Reduction in a Rechargeable Zn-Air Battery

The oxygen reduction/evolution reaction (ORR/OER) represents a pivotal process in metal-air batteries; however, it is constrained by the limitations of slow kinetics. Nevertheless, the creation of long-lasting and bifunctional catalysts represents a significant challenge. This study presents a series of hierarchical porous carbon-supported cobalt pyrophosphate (Co2P2O7-N/C-T) catalysts, prepared through the pyrolysis of porphyrin-based NTU-70 nanosheets with red phosphorus at varying temperatures. The Co2P2O7-N/C-800 not only demonstrates remarkable OER performance with an overpotential of only 290 mV at a current density of 10 mA cm-2 in 1 M KOH, but also exhibits an excellent ΔE of 0.74 V in 0.1 M KOH, which is lower than that of Pt/C + RuO2 (0.76 V). The utilization of Co2P2O7-N/C-800 as an air cathode in a rechargeable Zn-air battery (ZAB) results in a stable discharge voltage plateau of 1.405 V and a high gravimetric energy density of 801.2 mA h gZn-1. This work presents a promising strategy for the design of efficient bifunctional catalysts and demonstrates the critical importance of the interplay between the active center and the supported hierarchical porous carbon.

Multivalent Sulfur Vacancy-Rich NiCo2S4@MnO2 Urchin-Like Heterostructures for Ambient Electrochemical N2 Reduction to NH3

Innovative advances in the exploitation of effective electrocatalytic materials for the reduction of nitrogen (N2) to ammonia (NH3) are highly required for the sustainable production of fertilizers and zero-carbon emission fuel. In order to achieve zero-carbon footprints and renewable NH3 production, electrochemical N2 reduction reaction (NRR) provides a favorable energy-saving alternative but it requires more active, efficient, and selective catalysts. In current work, sulfur vacancy (Sv)-rich NiCo2S4@MnO2 heterostructures are efficaciously fabricated via a facile hydrothermal approach followed by heat treatment. The urchin-like Sv-NiCo2S4@MnO2 heterostructures serve as cathodes, which demonstrate an optimal NH3 yield of 57.31 µg h-1 mgcat -1 and Faradaic efficiency of 20.55% at -0.2 V versus reversible hydrogen electrode (RHE) in basic electrolyte owing to the synergistic interactions between Sv-NiCo2S4 and MnO2. Density functional theory (DFT) simulation further verifies that Co-sites of urchin-like Sv-NiCo2S4@MnO2 heterostructures are beneficial to lowering the energy threshold for N2 adsorption and successive protonation. Distinctive micro/nano-architectures exhibit high NRR electrocatalytic activities that might motivate researchers to explore and concentrate on the development of heterostructures for ambient electrocatalytic NH3 generation.

Real-time screening of NixBy bifunctional electrocatalysts for overall NH3 synthesis via SG-TC SECM

Electrochemical ammonia synthesis, which couples oxygen evolution at the anode with nitrogen reduction at the cathode, holds great significance for future food and energy needs. Both of these half-cell reactions determine the overall cell potential and efficiency of the process. However, the employment of different catalysts on either side, due to discrete mechanisms, increases the complexity and material processing costs of the system, where the designing of a bifunctional catalyst active towards both the NRR and OER is of huge significance. Unfortunately, the initial screening of the designed catalysts via physical characterizations, optical methods and other techniques, does not provide details about the electrochemical activity. The scanning electrochemical microscopy (SECM) technique can be useful to screen multi-catalysts at the same time for their electrochemical activities. Herein, we employed the sample generation-tip collection (SG-TC) mode of SECM to screen the designed NixBy catalysts before half-cell investigations, which suggested that the catalyst synthesized via sonochemical reduction (SR), i.e. NixBy (SR), was a better catalyst. This inference was in accordance with the half-cell NRR and OER measurements (FE: 49% for NH3 production, OER overpotential: 300 mV). By virtue of this remarkable bifunctional activity, the NRR-OER coupled full cell was assembled, which initiated the NH3 production at just 1.7 V and produced NH3 (1.08 mg h-1 mgcat-1) at the cathode and O2 (0.81 mg h-1 mgcat-1) at the anode after 2 h of electrolysis at 1.9 V.

Boosting nucleophilic attack to realize high current density biomass valorization on a tunable Prussian blue analogue

Electrochemical biomass valorization provides a promising approach to generating value-added chemicals. Herein, we have creatively utilized a Prussian blue analogue as a structure template of the anodic catalyst and improved its catalyst capacity by adjusting its electronic structure. The nickel-based Prussian blue analogue/Ni foam (NiFe-PBA/NF) exhibits excellent performance for methanol (MeOH) oxidation and achieves almost 94.1% FE of formic acid at a high current density of 500 mA cm-2. Apart from formic acid, NiFe-PBA/NF also has good catalytic ability for ethanol, glycerol, glucose, and 5-hydroxymethylfurfural (HMF). In short, this work has developed a promising class of catalysts for biomass valorization.