Trimetallic FeCoNi disulfide nanosheets for CO2-emission-free methanol conversion

Amorphous-microcrystalline heterostructured high-entropy oxysulfide/cerium oxide with strong electronic communication to boost water/simulated seawater splitting

Exploring bifunctional transition metal-based oxysulfide with high activities, corrosion resistance and reaction selectivity is a promising strategy to realize efficient water/seawater splitting. Here, amorphous, high entropy and heterostructure strategies are coupled to construct the amorphous-microcrystalline heterostructured high-entropy oxysulfide/cerium oxide (a-NiCoFeOS/c-CeO2) by one-step intermittent electrodeposition. With the strong interfacial electronic communication, a-NiCoFeOS/c-CeO2 shows high bifunctional activities with low overpotentials for hydrogen evolution reaction (47/63 mV) and oxygen evolution reaction (216/220 mV) at 10 mA cm-2 in alkaline water/simulated seawater, respectively. The a-NiCoFeOS/c-CeO2 (+, -)-assembled electrolyzers require low cell voltages of 1.54/1.58 V to attain the current density of 10 mA cm-2 for overall alkaline water/simulated seawater splitting. Moreover, a-NiCoFeOS/c-CeO2 exhibits strong activity retention and high Faradaic efficiency in alkaline water/simulated seawater. Significantly, a-NiCoFeOS/c-CeO2 (+, -) tolerates the industrial alkaline water splitting condition (500 mA cm-2 in 6 M KOH @ 60 °C) with a strong durability of 210 h. Surface-reconstructed Ni/Co/Fe-based hydroxides/oxyhydroxides guarantee the high activity retention during the stability testing. The permiselective c-CeO2 and adsorbed sulfate enhance reaction selectivity and corrosion resistance by the inhibition of Cl- approach. Herein, an innovative strategy is proposed for construction of efficient water/seawater electrocatalysts, showing great potential for industrial application.

Surface Selenium Coating Promotes Selective Methanol-to-Formate Electrooxidation on Ni3Se4 Nanoparticles

In the quest to replace fossil fuels and reduce carbon dioxide emissions, developing energy technologies based on clean catalytic processes is fundamental. However, the cost-effectiveness of these technologies strongly relies on the availability of efficient catalysts made of abundant elements. Herein, this study presents a one-step hydrothermal method to obtain a series of Ni3Se4 nanoparticles with a layer of amorphous selenium on their surface. When employed as electrocatalysts for the methanol oxidation reaction (MOR), the optimized proper surface Se-coated Ni3Se4 nanoparticles exhibit a high current density of 160 mA cm-2 at 1.6 V, achieving a high methanol-to-formate Faradaic efficiency above 97.8% and excellent stability with less than 20% current decay after an 18 h chronoamperometry test. This excellent performance is rationalized using density functional theory calculations, which unveil that the electrochemical recombination of SeOx results in a reduction of the energy barrier for the dehydrogenation of methanol during the MOR process.

Hydrothermal nickel selenides as efficient electrodes in alkaline media: application to supercapacitors and the methanol oxidation reaction

The advancement of active electrochemical materials is pivotal for enhancing energy conversion and storage technologies, which is essential for a sustainable future. Furthermore, achieving cost-effective technologies necessitates avoiding the use of noble metals and low-throughput processes that require high vacuum or high temperatures. Herein, we describe in detail a simple solution-based protocol to obtain a series of phase-controlled nickel selenide nanomaterials. The electrochemical performance of these materials, influenced by the phase and morphology, has been further analyzed. To showcase the application of these materials, two technologies are considered: (i) supercapacitors; and (ii) the methanol oxidation reaction (MOR). In particular, the Ni3Se4-based electrode in 1 M KOH shows an initial specific capacitance of 1903.5 F g-1 at a discharge current of 0.1 mA and displays a notable stability for over 3000 cycles. Furthermore, in an alkaline medium with methanol, this electrode produces a current density of 95.5 mA cm-2, facilitating methanol-to-formate conversion with a faradaic efficiency of up to 95.7% during a continuous 20-hour test. This research underscores the potential of nickel selenide nanomaterials in driving the next generation of energy storage and conversion technologies.

Nickel foam supported Mn-doped NiFe-LDH nanosheet arrays as efficient bifunctional electrocatalysts for methanol oxidation and hydrogen evolution

Electrochemical upgrading methanol into value-added formate at the anode in alkaline media enables the boosting production of hydrogen fuel at the cathode with saved energy. To achieve such a cost-effective and efficient electrocatalytic process, herein this work presents a Mn-doped nickel iron layered double hydroxides supported on nickel foam, derived from a simple hydrothermal synthesis. This developed electrocatalyst could act as an efficient bifunctional electrocatalyst for methanol-to-formate with a high faradaic efficiency of nearly 100 %, and for hydrogen evolution reaction, at an external potential of 1.5 V versus reversible hydrogen electrode. Additionally, a current density of 131.1 mA cm-2 with a decay of merely 12.2 % over 120 h continuous long-term testing was generated in co-electrocatalysis of water/methanol solution. Further density functional theoretical calculations were used to unravel the methanol-to-formate reaction mechanism arising from the doping of Fe and/or Mn. This work offers a good example of co-electrocatalysis to produce formate and green hydrogen fuel using a bifunctional electrocatalyst.

Selective Ethylene Glycol Oxidation to Formate on Nickel Selenide with Simultaneous Evolution of Hydrogen

There is an urgent need for cost-effective strategies to produce hydrogen from renewable net-zero carbon sources using renewable energies. In this context, the electrochemical hydrogen evolution reaction can be boosted by replacing the oxygen evolution reaction with the oxidation of small organic molecules, such as ethylene glycol (EG). EG is a particularly interesting organic liquid with two hydroxyl groups that can be transformed into a variety of C1 and C2 chemicals, depending on the catalyst and reaction conditions. Here, a catalyst is demonstrated for the selective EG oxidation reaction (EGOR) to formate on nickel selenide. The catalyst nanoparticle (NP) morphology and crystallographic phase are tuned to maximize its performance. The optimized NiS electrocatalyst requires just 1.395 V to drive a current density of 50 mA cm^-2 in 1 m potassium hydroxide (KOH) and 1 m EG. A combination of in situ electrochemical infrared absorption spectroscopy (IRAS) to monitor the electrocatalytic process and ex situ analysis of the electrolyte composition shows the main EGOR product is formate, with a Faradaic efficiency above 80%. Additionally, C2 chemicals such as glycolate and oxalate are detected and quantified as minor products. Density functional theory (DFT) calculations of the reaction process show the glycol-to-oxalate pathway to be favored via the glycolate formation, where the CC bond is broken and further electro-oxidized to formate.

Trimetallic non-noble NiCoSn alloy as an efficient electrocatalyst towards methanol oxidation and oxygen reduction reactions

The development of a non-noble, highly efficient bifunctional catalyst for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) is the bottleneck in the alkaline direct methanol fuel cells (ADMFC). Ni-based bi/tri metallic alloys are the promising candidates next to the noble metals in the alkaline medium.Herein we present a facile hydrazine-assisted hydrothermal technique to synthesize a trimetallic nickel-cobalt-tin (NiCoSn) alloy as an efficient electrocatalyst for MOR and ORR reactions. The physiochemical analysis confirms the formation of trimetallic alloys with a high surface area. The as-synthesized trimetallic NiCoSn electrocatalyst exhibited superior MOR activity in terms of mass activity (509 mA mg^-1 at 1.55 V vs RHE) and stability than the bimetallic alloys in 1.0 M KOH electrolyte. Further, the trimetallic alloy delivered a lower onset and half-wave potential of 0.8 and 0.72 V vs RHE with the favorable four-electron transfer in the oxygen reduction reactions. This work highlights a facile approach for preparing Ni-based trimetallic alloys as a promising candidate for the alkaline direct methanol fuel cells/other catalytic applications.

Ternary alloy (FeCoNi) nanoparticles supported on hollow porous carbon with defects for enhanced oxygen evolution reaction

Low-cost non-noble metal nanoparticles are promising electrocatalysts that can catalyze oxygen evolution reaction (OER). Various factors such as poor activity and stability hinder the practical applications of these materials. The electroactivity and durability of the electrocatalysts can be improved by optimizing the morphology and composition of the materials. Herein, we report the successful synthesis of hollow porous carbon (HPC) catalysts loaded with ternary alloy (FeCoNi) nanoparticles (HPC-FeCoNi) for efficient OER. HPC is firstly synthesized by a facile carbon deposition method using the hierarchical porous zeolite ZSM-5 as the hard template. Numerous defects are generated on the carbon shell during the removal of zeolite template. Subsequently, FeCoNi alloy nanoparticles are supported on HPC by a sequence of impregnation and H₂ reduction processes. The synergistic effect between carbon defects and FeCoNi alloy nanoparticles endows the catalyst with an excellent OER performance (low overpotential of 219 mV; Tafel slope of 60.1 mV dec^-1) in a solution of KOH (1 M). A stable potential is maintained during the continuous operation over 72 h. The designed HPC-FeCoNi presents a platform for the development of electrocatalysts that can be potentially applied for industrial OER.

Inhibitor and Activator: Dual Role of Subsurface Sulfide Enables Selective and Efficient Electro-Oxidation of Methanol to Formate on CuS@CuO Core-Shell Nanosheet Arrays

Selective electro-oxidation of aliphatic alcohols into value-added carboxylates at lower potentials than that of the oxygen evolution reaction (OER) is an environmentally and economically desirable anode reaction for clean energy storage and conversion technologies. However, it is challenging to achieve both high selectivity and high activity of the catalysts for the electro-oxidation of alcohols, such as the methanol oxidation reaction (MOR). Herein, a monolithic CuS@CuO/copper-foam electrode for the MOR with superior catalytic activity and almost 100% selectivity for formate is reported. In the core-shell CuS@CuO nanosheet arrays, the surface CuO directly catalyzes MOR, while the subsurface sulfide not only serves as an inhibitor to attenuate the oxidative power of the surface CuO to achieve selective oxidation of methanol to formate and prevent over-oxidation of formate to CO₂ but also serves as an activator to form more surface O defects as active sites and enhances the methanol adsorption and charge transfer to achieve superior catalytic activity. CuS@CuO/copper-foam electrodes can be prepared on a large scale by electro-oxidation of copper-foam at ambient conditions and can be readily utilized in clean energy technologies.