Nanostructured Carbon-Nitrogen-Sulfur-Nickel Networks Derived From Polyaniline as Bifunctional Catalysts for Water Splitting

Novel magnetic Fe@NSC nanohybrid material for arsenic removal from aqueous media

Polymer-derived carbon nanohybrids present a remarkable potential for the elimination of water pollutants. Herein, an Fe-modified C, N, and S (Fe@NSC) nanohybrid network, synthesized via polymerization of aniline followed by calcination, is used for As removal from aquatic media. The Langmuir isotherm and pseudo-second-order kinetic models fit well the experimental data for the adsorptive removal of As(III) and As(V) by the as-synthesized Fe@NSC nanohybrid, indicating that adsorption is a monolayer chemisorption process. The maximum adsorption capacities of the fabricated Fe@NSC nanohybrid for As(III) and As(V) were 129.54 and 178.65 mg/g, respectively, which are considerably higher than those reported previously for other adsorbents. In particular, the Fe₃O₄/FeS nanoparticles (18.4-38.7 nm) of the prepared Fe@NSC nanohybrid play a critical role in As adsorption and oxidation. Spectroscopy data indicate that the adsorption of As on Fe@NSC nanohybrid involved oxidation, ligand exchange, surface complexation, and electrostatic attraction. Furthermore, the magnetic Fe@NSC nanohybrid was easily separated after As adsorption using an external magnet and did not induce acute toxicity (48 h) in Daphnia magna. Moreover, the Fe@NSC nanohybrid selectively removed As species in the presence of competing anions and was effectively regenerated for up to three cycles using a 0.1 M HNO₃ solution. These findings suggest that Fe@NSC nanohybrid is a promising adsorbent for As remediation in aquatic media.

Synergistic Regulation of S-Vacancy of MoS2-Based Materials for Highly Efficient Electrocatalytic Hydrogen Evolution

Low or excessively high concentration of S-vacancy (C_S-vacancy) is disadvantageous for the hydrogen evolution reaction (HER) activity of MoS₂-based materials. Additionally, alkaline water electrolysis is most likely to be utilized in the industry. Consequently, it is of great importance for fine-tuning C_S-vacancy to significantly improve alkaline hydrogen evolution. Herein, we have developed a one-step Ru doping coupled to compositing with CoS₂ strategy to precisely regulate C_S-vacancy of MoS₂-based materials for highly efficient HER. In our strategy, Ru doping favors the heterogeneous nucleation and growth of CoS₂, which leads to a high crystallinity of Ru-doped CoS₂ (Ru-CoS₂) and rich heterogeneous interfaces between Ru-CoS₂ and Ru-doped MoS_2-x (Ru-MoS_2-x). This facilitates the electron transfer from Ru-CoS₂ to Ru-MoS_2-x, thereby increasing C_S-vacancy of MoS₂-based materials. Additionally, the electron injection effect increases gradually with an increase in the mass of Co precursor (m_Co), which implies more S^2- leaching from MoS₂ at higher m_Co. Subsequently, C_S-vacancy of the as-synthesized samples is precisely regulated by the synergistic engineering of Ru doping and compositing with CoS₂. At C_S-vacancy = 17.1%, a balance between the intrinsic activity and the number of exposed Mo atoms (EMAs) to boost highly active EMAs should be realized. Therefore, the typical samples demonstrate excellent alkaline HER activity, such as a low overpotential of 170 mV at 100 mA cm⁻² and a TOF of 4.29 s⁻¹ at -0.2 V. Our results show promise for important applications in the fields of electrocatalysis or energy conversion.

Insights on the Electrocatalytic Seawater Splitting at Heterogeneous Nickel-Cobalt Based Electrocatalysts Engineered from Oxidative Aniline Polymerization and Calcination

Given the limited access to freshwater compared to seawater, a growing interest surrounds the direct seawater electrolysis to produce hydrogen. However, we currently lack efficient electrocatalysts to selectively perform the oxygen evolution reaction (OER) over the oxidation of the chloride ions that are the main components of seawater. In this contribution, we report an engineering strategy to synthesize heterogeneous electrocatalysts by the simultaneous formation of separate chalcogenides of nickel (NiS_x, x = 0, 2/3, 8/9, and 4/3) and cobalt (CoS_x, x = 0 and 8/9) onto a carbon-nitrogen-sulfur nanostructured network. Specifically, the oxidative aniline polymerization in the presence of metallic cations was combined with the calcination to regulate the separate formation of various self-supported phases in order to target the multifunctional applicability as both hydrogen evolution reaction (HER) and OER in a simulated alkaline seawater. The OER’s metric current densities of 10 and 100 mA cm⁻² were achieved at the bimetallic for only 1.60 and 1.63 V_RHE, respectively. This high-performance was maintained in the electrolysis with a starting voltage of 1.6 V and satisfactory stability at 100 mA over 17 h. Our findings validate a high selectivity for OER of ~100%, which outperforms the previously reported data of 87–95%.

Iridium and Ruthenium Modified Polyaniline Polymer Leads to Nanostructured Electrocatalysts with High Performance Regarding Water Splitting

The breakthrough in water electrolysis technology for the sustainable production of H₂, considered as a future fuel, is currently hampered by the development of tough electrocatalytic materials. We report a new strategy of fabricating conducting polymer-derived nanostructured materials to accelerate the electrocatalytic hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and water splitting. Extended physical (XRD, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX)) and electrochemical (cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS)) methods were merged to precisely characterize the as-synthesized iridium and ruthenium modified polyaniline (PANI) materials and interrogate their efficiency. The presence of Ir(+III) cations during polymerization leads to the formation of Ir metal nanoparticles, while Ru(+III) induces the formation of RuO₂ oxide nanoparticles by thermal treatment; they are therefore methods for the on-demand production of oxide or metal nanostructured electrocatalysts. The findings from using 0.5 M H₂SO₄ highlight an ultrafast electrochemical kinetic of the material PANI-Ir for HER (36 - 0 = 36 mV overpotential to reach 10 mA cm^-2 at 21 mV dec^-1), and of PANI-Ru for OER (1.47 - 1.23 = 240 mV overpotential to reach 10 mA cm^-2 at 47 mV dec^-1), resulting in an efficient water splitting exactly at its thermoneutral cell voltage of 1.45 V, and satisfactory durability (96 h).