FeNi nanoparticles embedded porous nitrogen-doped nanocarbon as efficient electrocatalyst for oxygen evolution reaction

Valence State and Catalytic Activity of Ni-Fe Oxide Embedded in Carbon Nanotube Catalysts

The catalytic activity of Ni-Fe oxide embedded in CNTs was investigated in terms of valence states and active oxygen species. Ni-Fe oxides were prepared by the sol-gel combustion process, and Ni-Fe oxides embedded in CNT catalysts were synthesized by the catalytic chemical vapor deposition (CCVD) method. The lattice structure of the Ni-Fe oxide catalysts was analyzed, and the lattice distortion was increased with the addition of Fe. The specific surface areas and pore structures of the Ni-Fe oxides embedded in CNTs were determined through the BET method. The nano-sized Ni-Fe oxides embedded in CNTs were observed using morphology analysis. The crystallinity and defects of CNTs were analyzed by Raman spectroscopy, and the ID/IG ratio of Ni1.25Fe0.75O/CNT was the lowest at 0.36, representing the high graphitization and low structural defects of the CNT surface. The valence states of Fe and Ni were changed by the interaction between catalysts and CNTs. The redox property of the catalysts was evaluated by H2-TPR analysis, and the H2 consumption of Ni1.25Fe0.75O/CNT was the highest at 2.764 mmol/g. The catalytic activity of Ni-Fe oxide embedded in CNT exhibited much higher activity than Ni-Fe oxide for the selective catalytic reduction of NOx with NH3 in the temperature range of 100 °C to 450 °C.

Template free-synthesis of cobalt-iron chalcogenides [Co0.8Fe0.2L2, L = S, Se] and their robust bifunctional electrocatalysis for the water splitting reaction and Cr(vi) reduction

The ease of production of materials and showing multiple applications are appealing in this modern era of advanced technology. This paper reports the synthesis of a pair of novel cobalt-iron chalcogenides [Co0.8Fe0.2S2 and Co0.8Fe0.2Se2] with enhanced electro catalytic activities. These ternary metal chalcogenides were synthesized by a one-step template-free approach via a hexamethyldisilazane (HMDS)-assisted synthetic method. Transient photocurrent (TPC) studies and electrochemical impedance spectra (EIS) of these materials showed free electron mobility. Their bifunctional activities were verified in both the electrochemical oxygen evolution reaction (OER) and in the electrochemical reduction of toxic inorganic heavy metal ions [Cr(vi)] in polluted water. The materials showed robust catalytic ability in the oxygen evolution reaction with minimum possible over potential (345 and 350 mV @ η10) as determined by linear sweep voltammetry and the lower Tafel values (52.4 and 84.5 mV dec-1) for Co0.8Fe0.2Se2 and Co0.8Fe0.2S2 respectively. Surprisingly, both the materials also showed an excellent activity towards electrochemical Cr(vi) reduction to Cr(iii). Besides the maximum current achieved for Co0.8Fe0.2S2, a minimum value for the Limit of detection (LOD) was obtained for Co0.8Fe0.2S2 (0.159 μg L-1) compared to Co0.8Fe0.2Se2 (0.196 μg L-1). We tested the durability of catalysts, the critical factor for the prolonged use of catalysts, through the recyclability measurements of these materials as catalysts. Both the catalysts presented outstanding durability and balanced electro catalytic activities for up to 1500 CV cycles, and chronoamperometry studies also confirmed exceptional stability. The enhanced catalytic activities of these materials are ascribed to the free electron movement, evidenced by the increased TPC measured and EIS. Therefore, the template-free synthesis of these electro catalysts containing non-noble metal illustrates the practical approach to develop such types of catalysts for multiple functions.

Rationally Designed Ag@polymer@2-D LDH Nanoflakes for Bifunctional Efficient Electrochemical Sensing of 4-Nitrophenol and Water Oxidation Reaction

The rational design and demonstration of a facile sequential template-mediated strategy to construct noble-metal-free efficient bifunctional electrocatalysts for efficient oxygen evolution reaction (OER) and electrocatalytic detection of hazardous environmental 4-nitrophenol (4-NP) have continued as a major challenging task. Herein, we construct a novel Ag@polymer/NiAl LDH (designated as APL) nanohybrid as an efficient bifunctional electrocatalyst by a simple hydrolysis method. The well-fabricated APL/GCE exhibited an extensive linear range from 0.1 to 100 μM in optimized conditions. It showed a detection limit (LOD) of 0.0096 μM (9.6 nM) (S/N = 3) for 4-NP in pH 6 by differential pulse voltammetry (DPV). Meanwhile, the newly fabricated APL exhibited outstanding OER activity with a very low overpotential of 259 mV to deliver 10 mA cm^-2 current density (J) at a scan rate of 5 mV/s. The Tafel plot value of APL is low (97 mV/dec) compared to that of the benchmark RuO₂ due to a fast kinetic reaction. Besides, the durability of the electrocatalyst was assessed by a chronoamperometry test (CA) for 36 h at 1.55 mV vs RHE, and the long-term cycling stability was analyzed by using cyclic voltammetry (CV); after 5000 cycles, the electrocatalyst was highly stable. These demonstrated results could lead to an alternative electrocatalyst construction for the bifunctionally efficient electrochemical sensing of 4-nitrophenol and oxygen evolution reaction.

Oxygen-evolution reactions (OER) on transition-metal-doped Fe3Co(PO4)4 iron-phosphate surfaces: a first-principles study

A series of transition-metal-doped Fe_1−xM_xCo(PO₄)₄(010) and Fe₃Co_1−xM_x(PO₄)₄(010) electro-catalyst surfaces (with M = Mn, Os, Ru, Rh and Ir) have been modelled via density-functional theory (DFT) to gauge their oxygen-evolution reactions (OER).

FeNi3-modified Fe2O3/NiO/MoO2 heterogeneous nanoparticles immobilized on N, P co-doped CNT as an efficient and stable electrocatalyst for water oxidation

As a rate-determining step, electrocatalytic water oxidation acts a pivotal role in the water splitting process. As a consequence, it is of great significance to explore low-cost, efficient and durable electrocatalysts for the oxygen evolution reaction (OER) to promote electrocatalytic splitting water. Herein, for the first time, FeNi₃-modified Fe₂O₃/NiO/MoO₂ heterogeneous nanoparticles immobilized on N, P co-doped CNT matrix materials (FNM/NPCNT) are synthesized via a facile solid-phase grinding of the precursor, composed of nickel hexacyanoferrate/phosphomolybdic acid/CNT, and subsequently pyrolyzing under nitrogen atmosphere without any further post-processing. Due to its significant enhancement of the charge transfer efficiency and prevention of the metallic-based catalysts from being corroded, the as-prepared FNM/NPCNT hybrid electrocatalyst shows a high OER activity with a low overpotential of 282 mV vs. RHE at 10 mA cm^-2 and a small Tafel slope of 46.2 mV dec^-1 in an alkaline electrolyte. Moreover, the as-prepared FNM/NPCNT hybrid delivers a large mass activity of 327.6 A g^-1 at the potential of 1.7 V and excellent stability (more than 20 h). This study opens up a new approach to design and synthesize non-precious transition metal-based composites immobilized N, P co-doped CNT materials as OER catalysts with high efficiency and long-term stability for promoting water splitting.

FexNiy/CeO2 loaded on N-doped nanocarbon as an advanced bifunctional electrocatalyst for the overall water splitting

The synergy of each component in the Fe_xNi_y/CeO₂/NC renders outstanding electrocatalytic activities and stability toward the HER and OER.