Mimicking Hydrazine Dehydrogenase for Efficient Electrocatalytic Oxidation of N2H4 by Fe-NC

Enhanced fluoride removal in a novel magnesium-carbon micro-electrolysis constructed wetland through accelerated electron transport and anodic sacrifice

High fluoride (F-) content in the aquatic environment is a significant‌ issue affecting public health. Constructed wetlands (CWs) are believed to have unique potential for alleviating F- pollution in the aquatic environment. In this study, magnesium (Mg) and iron/nitrogen co-doped biochar (FeNBC) was used as the filler of a novel micro-electrolysis constructed wetland (WNME). Compared with the control, WNME significantly enhanced the F- removal efficiency from 19.1 ± 7.3 % to 54.1 ± 8.3 %, in which 90.7 % of total F- removal in WNME was attributed to the micro-electrolysis filler. The enhancement was attributed to the co-doping of iron and nitrogen, which improved the surface morphology, element distribution, and electrochemical performance of FeNBC. This led to an increase in the potential of FeNBC by 9.8 %, thereby increasing the potential difference within the Mg-C micro-electrolysis system. The Mg2+ release from anodic sacrifice in WNME was promoted, which led to an increase in MgF2 as the precipitate. Micro-electrolysis promoted the enrichment of electrochemically active bacteria in WNME, resulting in enhanced electron transfer and high F- removal efficiency. This study provided new insights for F- removal in CWs and would shed light on the optimization of micro-electrolysis CWs for F- removal from the aqueous phase.

Electrocatalytic N-H bond transformations: a zero-carbon paradigm for sustainable energy storage and conversion

With the escalating challenges of environmental pollution and energy scarcity, the exploration of novel energy storage and conversion systems has become imperative. In contrast to traditional energy systems centered on C-H bonds, electrocatalytic energy systems based on N-H bonds offer a transformative approach by circumventing the limitations of carbon cycles and enabling a complete cycle from energy storage to conversion. This review comprehensively introduces the concept and advantages of zero-carbon energy systems based on electrocatalytic N-H bond formation and cleavage. We delve into the reaction mechanisms of key electrocatalytic processes within these systems, along with the development and applications of associated electrocatalysts. Finally, we discuss the development prospect and challenges of zero-carbon energy systems based on the N-H bond, which provides guidance for the application of clean energy storage and conversion.

A dual-color ESIPT-based probe for simultaneous detection of hydrogen sulfide and hydrazine

Hydrogen sulfide (H2S) and hydrazine (N2H4) are toxic compounds in environmental and living systems, and hydrogen sulfide is also an important signaling molecule. However, in the absence of dual-color probes capable of detecting both H2S and N2H4, the ability to monitor the crosstalk of these substances is restricted. Herein, we developed an ESIPT-based dual-response fluorescent probe (BDM-DNP) for H2S and N2H4 detection via dually responsive sites. The BDM-DNP possessed absorbing strength in the detection of H2S and N2H4, with a large Stokes shift (156 nm for H2S and 108 nm for N2H4), high selectivity and sensitivity, and good biocompatibility. Furthermore, BDM-DNP can be utilized for the detection of hydrogen sulfide and hydrazine in actual soil, and gaseous H2S and N2H4 in environmental systems. Notably, BDM-DNP can detect H2S and N2H4 in living cells for disease diagnosis and treatment evaluation.

Design of a ratiometric near-infrared fluorescent probe with double excitation for hydrazine detection in vitro and in vivo

Hydrazine has a wide range of industrial applications, but it is also a toxic and explosive chemical substance, which brings potential risks to human health and environmental safety. Therefore, rapid and sensitive monitoring of hydrazine is of great importance in environmental sciences and biological systems. In this work, a new near-infrared (NIR) ratiometric fluorescent probe (Ac-HY) was designed to detect hydrazine under double excitation and emission mode. Ac-HY exhibited large stokes shift (130 nm), high selectivity and sensitivity to hydrazine detection. The applications of Ac-HY probe for detecting hydrazine in vapor and imaging hydrazine in lipid droplets and zebrafish. Therefore, Ac-HY can be used to monitor the distribution of exogenous hydrazine in vitro and in vivo.

Understanding hydrazine oxidation electrocatalysis on undoped carbon

Carbons are ubiquitous electrocatalytic supports for various energy-related transformations, especially in fuel cells. Doped carbons such as Fe-N-C materials are particularly active towards the oxidation of hydrazine, an alternative fuel and hydrogen carrier. However, there is little discussion of the electrocatalytic role of the most abundant component - the carbon matrix - towards the hydrazine oxidation reaction (HzOR). We present a systematic investigation of undoped graphitic carbons towards the HzOR in alkaline electrolyte. Using highly oriented pyrolytic graphite electrodes, as well as graphite powders enriched in either basal planes or edge defects, we demonstrate that edge defects are the most active catalytic sites during hydrazine oxidation electrocatalysis. Theoretical DFT calculations support and explain the mechanism of HzOR on carbon edges, identifying unsaturated graphene armchair defects as the most likely active sites. Finally, these findings explain the 'double peak' voltammetric feature observed on many doped carbons during the HzOR.

Fe-N-C electrocatalysts in the oxygen and nitrogen cycles in alkaline media: the role of iron carbide

Fe-N-C electrocatalysts hold a great promise for Pt-free energy conversion, driving the electrocatalysis of oxygen reduction and evolution, oxidation of nitrogen fuels, and reduction of N₂, CO₂, and NO_x. Nevertheless, the catalytic role of iron carbide, a component of nearly every pyrolytic Fe-N-C material, is at the focus of a heated controversy. We now resolve the debate by examining a broad range of Fe₃C sites, spanning across many typical size distributions and carbon environments. Removing Fe₃C selectively by a non-oxidizing acid reveals its inactivity towards two representative reactions in alkaline media, oxygen reduction and hydrazine oxidation. The activity is assigned to other pre-existing sites, most probably Fe-N_x. DFT calculations prove that the Fe₃C surface binds O and N intermediates too strongly to be catalytic. By settling the argument on the catalytic role of Fe₃C in alkaline electrocatalysis, we hope to spur innovation in this critical field.

Ultrafine Co6W6C as an efficient anode catalyst for direct hydrazine fuel cells

Ultrafine ternary carbide Co₆W₆C@C nanoparticles (NPs) were successfully synthesized and these NPs exhibited high catalytic activities for the hydrazine oxidation reaction (HzOR) under alkaline conditions. In a practical O₂-hydrazine fuel cell test, its peak power density reached 203 mW cm^-2, a value superior to that of the state-of-the-art commercial Pt/C catalyst.

Template-Free Formation of Regular Macroporosity in Carbon Materials Made from a Folded Polymer Precursor

Porous carbon materials attract great interest in a wide range of applications such as batteries, fuel cells, and membranes, due to their large surface area, structural and compositional tunability, and chemical stability. While micropores are typically obtained when preparing carbon materials by pyrolysis, the fabrication of mesoporous, and especially macroporous carbons is more challenging, yet important for enhancing mass transport. Herein, template-free regular macroporous carbons are prepared from a mixture of unfolded (linear) and folded (single-chain nanoparticles, SCNP) polyvinylpyrrolidone chains. While having the same chemical composition, the different molecular architectures lead to phase separation even before pyrolysis, creating a dense cell architecture, which is retained upon carbonization. Upon increasing the SCNP content, the homogeneity of the pore network increases and the specific surface area is enlarged 3-5-fold, until ideal properties are obtained at 75% SCNP, as observed by high-resolution scanning electron microscopy and N₂ physisorption porosimetry. The materials are further investigated as hydrazine oxidation electrocatalysts, demonstrating the link between the evolving morphology and current density. Importantly, this study demonstrates the role of polymer architecture in macroporosity templating in carbon materials, providing a new approach to develop complex carbon architectures without the need for external templating.

Bifunctional single-atomic Mn sites for energy-efficient hydrogen production

The electrocatalytic hydrogen evolution reaction (HER) for H2 production is essential for future renewable and clean energy technology. Screening energy-saving, low-cost, and highly active catalysts efficiently, however, is still a grand challenge due to the sluggish kinetics of the oxygen evolution reaction (OER) in electrolyzing water. Herein, we present a single atomic Mn site anchored on a boron nitrogen co-doped carbon nanotube array (Mn-SA/BNC), which is perfectly combined with the hydrazine electrooxidation reaction (HzOR) boosted water electrolysis concept. The obtained catalyst achieves 51 mV overpotential at the current density of -10 mA cm-2 for the cathodic HER and 132 mV versus the reversible hydrogen electrode for HzOR, respectively. Besides, in a two-electrode overall hydrazine splitting (OHzS) system, the Mn-SA/BNC catalyst only needs a cell voltage of only 0.41 V to output 10 mA cm-1, with strong durability and nearly 100% faradaic efficiency for H2 production. This work highlights a low-cost and high-efficiency energy-saving H2 production pathway.

In Situ Electrochemical Fabrication of Ultrasmall Ru-Based Nanoparticles for Robust N2H4 Oxidation

Ultrasmall Ru nanoparticles is expected as a potential alternative to Pt for efficient hydrazine oxidation (HzOR). However, preparation of ultrasmall and well-distributed Ru nanoparticles usually suffered from the steps of modification of supports, coordination, reduction with strong reducing reagents (e.g., NaBH₄) or pyrolysis, imposing the complexity. Based on the self-reducibility of C-OH group and physical adsorption ability of commercial Ketjen black (KB), we developed an efficient, stable and robust Ru-based electrocatalyst (A-Ru-KB) by coupling impregnation of KB in RuCl₃ solution and simple in situ electrochemical activation strategy, which endowed the formation of ultrasmall and well-distributed Ru nanoparticles. Benefiting from an enhanced exposure of Ru sites and the faster mass transport, A-Ru-KB achieved 63.4 and 3.9-fold enhancements of mass activity compared with Pt/C and Ru/C, respectively, accompanied by a ∼144 mV lower onset potential and faster catalytic kinetics than Pt/C. In the hydrazine fuel cell, the open-circuit voltage and maximal mass power density of A-Ru-KB was 130 mV and ∼3.8-fold higher than those of Pt/C, respectively, together with the long-term stability. This work would provide a facile and sustainable approach for large-scale production of other robust metal (electro)catalysts with ultrasmall nanosize for various energy conversion and electrochemical organic synthesis.