Ir nanoclusters/porous N-doped carbon as a bifunctional electrocatalyst for hydrogen evolution and hydrazine oxidation reactions

Highly bifunctional Rh2P on N,P-codoped carbon for hydrazine oxidation assisted energy-saving hydrogen production

Highly pure Rh2P nanoparticles on N,P-codoped carbon were synthesized by a simple "mix-and-pyrolyze" method using one kind of low-cost nucleotide as the carbon, nitrogen and phosphorus source, which exhibits excellent bifunctional activity for the hydrogen reduction and hydrazine oxidation reactions, achieving energy-efficient hydrogen production.

Highly enhanced hydrazine oxidation on bifunctional Ni tailored by alloying for energy-efficient hydrogen production

The low-potential hydrazine oxidation reaction (HzOR) can replace the oxygen evolution reaction (OER) and thus assemble with the hydrogen evolution reaction (HER), consequently achieving energy-saving hydrogen (H2) production. Notably, developing sophisticated bifunctional electrocatalysts for HER and HzOR is a prerequisite for efficient H2 production. Alloying noble metals with eligible non-precious ones can increase affordability, catalytic activity, and stability, alongside rendering bifunctionality. Herein, RuNi alloy deposited onto carbon (RuNi/C) was directly prepared by a simple and highly practical co-reduction method, showing excellent performance for HER and HzOR. Interestingly, to achieve 10 mA cm-2, RuNi/C only required an ultralow potential of 24 mV for HER, on par with commercial 20 wt% platinum in carbon (Pt/C), and -65 mV for HzOR, surpassing most reported counterparts. Moreover, the two-electrode electrolyzer only required small operation voltages of 57.8 and 327 mV to drive 10 and 100 mA cm-2, respectively. Driven by a homemade hydrazine (N2H4) fuel cell and solar panel, appreciable H2 yields of 1.027 and 1.406 mmol h-1 were achieved, respectively, exhibiting the energy-saving advantages alongside robust practicability. Moreover, theoretical calculations revealed that alloying with Ru endows bifunctional Ni sites not only with a lower H2O dissociation barrier but also with more favorable H* adsorption alongside the reduced energy barrier between HzOR intermediates.

Robust and Highly Efficient Electrochemical Hydrogen Production from Hydrazine-Assisted Water Electrolysis Enabled by the Metal-Support Interaction of Ru/C Composites

Hydrazine oxidation-assisted water electrolysis provides a promising way for the energy-efficient electrochemical hydrogen (H₂) and synchronous decomposition of hydrazine-rich wastewater, but the development of highly active catalysts still remains a great challenge. Here, we demonstrate the robust and highly active Ru nanoparticles supported on the hollow N-doped carbon microtube (denoted as Ru NPs/H-NCMT) composite structure as HER and HzOR bifunctional electrocatalysts. Thanks to such unique hierarchical architectures, the as-synthesized Ru NPs/H-NCMTs exhibit prominent electrocatalytic activity in the alkaline condition, which needs a low overpotential of 29 mV at 10 mA cm^-2 for HER and an ultrasmall working potential of -0.06 V (vs RHE) to attain the same current density for HzOR. In addition, assembling a two-electrode hybrid electrolyzer using as-prepared Ru NPs/H-NCMT catalysts shows a small cell voltage of mere 0.108 V at 100 mA cm^-2, as well as the remarkable long-term stability. Density functional theory calculations further reveal that the Ru NPs serve as the active sites for both the HER and HzOR in the nanocomposite, which facilitates the adsorption of H atoms and hydrazine dehydrogenation kinetics, thus enhancing the performances of HER and HzOR. This work paves a novel avenue to develop efficient and stable electrocatalysts toward HER and HzOR that promises energy-saving hybrid water electrolysis electrochemical H₂ production.

Ultrawide Hydrazine Concentration Monitoring Sensor Comprising Ir-Ni Nanoparticles Decorated with Multi-Walled Carbon Nanotubes in On-Site Alkaline Fuel Cell Operation

A highly sensitive amperometric hydrazine monitoring sensor offering an ultrawide dynamic range of 5 μM to 1 M in alkaline media (e. g., 1 M KOH) was developed via co-electrodepositing iridium-nickel alloy nanoparticles (NPs) functionalized with multi-walled carbon nanotubes (Ir-Ni-MWCNTs) on a disposable screen-printed carbon electrode. The synergistic interaction of MWCNTs with Ir-Ni alloy NPs resulted in enlarged active surface area, rapid electron transfer, and alkaline media stability with an onset potential of -0.12 V (vs. Ag/AgCl) toward hydrazine oxidation. A limit of detection for hydrazine was 0.81 μM with guaranteed reproducibility, repeatability, and storage stability alongside a superb selectivity toward ethanolamine, urea, dopamine, NaBH₄ , NH₄ OH, NaNO₂ , and Na₂ CO₃ . The sensor was finally applied to on-site monitoring of the carbon-free hydrazine concentration at the anode and cathode of a hydrazine fuel cell, providing more insight into the hydrazine oxidation process during cell operation.

Markedly boosted peroxymonosulfate- and periodate-based Fenton-like activities of iron clusters on sulfur/nitrogen codoped carbon: Key roles of a sulfur dopant and compared activation mechanisms

Highly dispersed iron nanoclusters on carbon (FeNC@C) hold great promise for wastewater purification in Fenton-like reactions. The microenvironment engineering of central Fe atom is promising to boost the activation capacity of FeNC@C, which is however remains a challenge. This study developed a self-sacrificed templating strategy to S, N-codoped carbon supported Fe nanoclusters (FeNC@SNC) activator and find the key role of sulfur heteroatoms in regulating the electron structure of Fe sites and final activation property. Investigations revealed that the FeNC@SNC composite exhibited unusual bifunctional activity in both peroxymonosulfate (PMS)- and periodate (PI)-based Fenton-like reactions. We also offered insights into the differences between the degradation of organics by the FeNC@SNC/PMS and FeNC@SNC/PI systems. Specifically, under identical conditions, the FeNC@SNC/PMS system delivered a higher oxidation capability and stronger resistance to nontarget matrix constituents, but showed more severe Fe leaching than the FeNC@SNC/PI system. Furthermore, while mediated electron-transfer process was identified as the major route for pollutant decomposition in both systems, the high-valent Fe-oxo species [Fe (IV)] was the auxiliary reactive species found only in the FeNC@SNC/PMS system. Based on these findings, our results provide profound insights into the design of active and durable Fe-based activators toward highly efficient Fenton-like reactions.