Voltage activation induced MoO42- dissolution to enhance performance of iron doped nickel molybdate for oxygen evolution reaction

Transition metal-based precatalysts are typically voltage-activated before electrochemical testing in the condition of alkaline oxygen evolution reaction. Nevertheless, the impact of voltage on the catalyst and the anion dissolution is frequently disregarded. In this study, Fe-doped NiMoO4 (Fe-NiMoO4) was synthesized as a precursor through a straightforward hydrothermal method, and MoFe-modified Ni (oxygen) hydroxide (MoFe-NiOxHy) was obtained via cyclic voltammetry (CV) activation. The effects of voltage on Fe-NiMoO4 and the dissolved inactive MoO42- ions in the process were examined in relation to OER performance. It has demonstrated that the crystallinity of the catalyst is reduced by voltage, thereby enhancing its electrocatalytic activity. The electron distribution state can be adjusted during the application of voltage, leading to the generation of additional active sites and an acceleration in the reaction rate. Additionally, MoO42- exhibits potential dependence during its dissolution. In the OER process, the dissolution of MoO42- enhances the reconstruction degree of Fe-NiMoO4 into the active substance and expedites the formation of active Ni(Fe)OOH. Hence, the optimized MoFe-NiOxHy exhibited exceptional electrocatalytic performance, with a current density of 100 mA cm-2 achieved at an overpotential of only 256 mV. This discovery contributes to a more comprehensive understanding of alkaline OER performance under the influence of applied voltage and the presence of inactive oxygen ions, offering a promising avenue for the development of efficient electrocatalysts.

Porous Fe5Si3 intermetallic anode for the oxygen evolution reaction in acidic electrolytes

Here, we show that a reactive synthesis method of mixed elemental powders can be used to synthesize a porous electrode consisting of an intermetallic Fe₅Si₃ that exhibits catalytic activity towards oxygen evolution reaction (OER) in acidic solutions, which is capable of delivering 10 mA cm^-2 at an overpotential of 0.73 V and a small Tafel slope of ~ 381.8 mV dec^-1. The amorphous silica formed in the anode surface during the electrochemical process is multifunctional, as it protects the electrode substrate from corrosion and acts as electrocatalysts for OER. Remarkably, the Si-based intermetallics can be generalized to include other OER catalytic elements (Mn, Fe, Co), including Mn-Si and Co-Si intermetallics.

Insight into the amorphous nickel-iron (oxy)hydroxide catalyst for efficient oxygen evolution reaction

The specific roles of Ni and Fe in nickel-iron (oxy)hydroxide catalyst (NiFeO_x(OH)_y) are extensively discussed during oxygen evolution reaction (OER). However, there still remains controversy about whether Ni or Fe species as the dominate active site. In this work, we reported the NiFeO_x(OH)_y catalysts with varied atomic ratio of nickel and iron for OER to explore the dominate active site during OER processes. From the electrochemical performances, the similar Tafel slopes of catalysts with Fe species can achieve at a level of 40 mV dec^-1, outperforming the Tafel slopes of catalysts without Fe species. Thus, it can be concluded that the present Fe site can serve as the dominant active site in NiFeO_x(OH)_y for OER. Meanwhile, the Ni species is proved as the OH^- adsorption site, which is beneficial to the Fe site to deliver a better OER performance. As a result, the catalyst with an optimal Ni/Fe interface (atomic ratio of 1 : 1.18) displays outstanding OER performances. It only requires a low overpotential of 250 mV to deliver current density of 10 mA cm^-2 and exhibits a small Tafel slope of 39 mV dec^-1. This catalyst also shows remarkable stability with negligible potential decay after 50 h at a current density of 50 mA cm^-2. This work offers a new sight into the specific roles of Ni and Fe in NiFeO_x(OH)_y for OER.

Amorphous cobalt boride nanosheets anchored surface-functionalized carbon nanofiber: An bifunctional and efficient catalyst for electrochemical sensing and oxygen evolution reaction

Development of new metal boride with carbon composite is an emerging class of catalyst and it brings enormous curiosity in the material community because of their potential intriguing properties. Here, we describe a new type of amorphous cobalt boride (A-CoB) nanosheet anchored on the surface of functionalized carbon nanofiber (A-CoB/ƒ-CNF) by a simple method. The emerged A-CoB/ƒ-CNF composite was demonstrated to possess great bifunctional electrocatalytic activity for the electrochemical sensing of antibiotic drug nitrofurantoin (NFT) and oxygen evolution reaction (OER). The prepared A-CoB/ƒ-CNF composite was characterized by various analytical and spectroscopic techniques such as XRD, FE-SEM, HR-TEM, Raman, and XPS analysis. The result from the electrochemical impedance spectroscopy confirms that the A-CoB/ƒ-CNF composite shows high electrical conductivity and the number of electron transferability for the NFT sensor and OER which is due to the presence of abundant active sites/large surface area in A-CoB, and synergistic effect between the A-CoB and ƒ-CNF. As an electrochemical sensor, the A-CoB/ƒ-CNF modified electrode shows substantial sensitivity (3.13 μA μM^-1 cm^-2), wider linear response range (0.01- 527 μM), and lower detection limit (0.003 μM) as-compared to the previously reported noble and non-noble metal-based electrocatalyst for NFT sensor. As well, the A-CoB/ƒ-CNF composite demonstrates superior OER activity with low overpotential and small Tafel slope value of 0.35 V and 173 mV/dec, respectively, which shows advanced kinetics than noble metal catalysts. Based on the results, we believed that the present work gives clear evidence for the preparation of transition metal boride anchored carbon material with an outstanding catalytic activity, and hence, it can be also extended to further electrochemical applications.