Energy-saving H2 Generation Coupled with Oxidative Alcohol Refining over Bimetallic Phosphide Ni2 P-CoP Junction Bifunctional Electrocatalysts

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.

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.

Anion-modulated CoP electrode as bifunctional electrocatalyst for anion-exchange membrane hydrazine-assisted water electrolyser

The hydrazine oxidation reaction (HzOR) is considered as a promising alternative process of the oxygen evolution reaction (OER) to realize more energy-efficient hydrogen generation. However, the lack of highly active bifunctional catalysts poses a huge challenge to this strategy. In this work, we report a novel and universal electrodeposition strategy to rationally synthesize a self-supporting electrode. The utilization of ammonium fluoride helps to modulate not only the morphology of CoP, but also the synchronous formation of an anion-modified structure, leading to an excellent bifunctional performance. The optimal F-CoP/CF exhibits small potentials of -90 mV and 41 mV at 1 A cm-2, high stability and low Tafel slopes of 28 mV dec-1 and 3.26 mV dec-1 for the HER and HzOR, respectively. The highly efficient and stable bifunctional activity of F-CoP/CF can be further confirmed in an anion-exchange membrane hydrazine-assisted water electrolyzer (0.49 V at 1 A cm-2). Utilizing the density functional theory calculations, the optimized adsorption energy of water molecules and hydrogen intermediates of the HER as well as the rate-determining step of the HzOR are demonstrated for the F-CoP.

Crystalline/amorphous composite interface of CoP@Ni/Fe-P as a boosted electrocatalyst for full water splitting

Heterojunction materials have become good candidates for electrocatalysts thanks to their unique physicochemical merits. Herein, a crystalline-amorphous CoP@Ni/Fe-P heterojunction is constructed for whole water splitting. Originating from the strong electronic reaction at the amorphous-crystal interfaces, the electron density of Co, Ni, Fe and P is adjusted, which will optimize the adsorption and desorption energy of intermediates for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) and lower the kinetic barrier. The CoP@Ni/Fe-P heterojunction displays overpotentials of 125 and 250 mV to drive a current density of 10 mA cm-2 in 1 M KOH. In addition, the whole water splitting performance requires a cell voltage of 1.56 V to deliver 10 mA cm-2 and shows good stability. This work provides a way to design and prepare transition-metal-based materials with good electrocatalytic activity by constructing a crystalline and amorphous heterojunction.

Essential role of lattice oxygen in methanol electrochemical refinery toward formate

Developing technologies based on the concept of methanol electrochemical refinery (e-refinery) is promising for carbon-neutral chemical manufacturing. However, a lack of mechanism understanding and material properties that control the methanol e-refinery catalytic performances hinders the discovery of efficient catalysts. Here, using 18O isotope-labeled catalysts, we find that the oxygen atoms in formate generated during the methanol e-refinery reaction can originate from the catalysts' lattice oxygen and the O-2p-band center levels can serve as an effective descriptor to predict the catalytic performance of the catalysts, namely, the formate production rates and Faradaic efficiencies. Moreover, the identified descriptor is consolidated by additional catalysts and theoretical mechanisms from density functional theory. This work provides direct experimental evidence of lattice oxygen participation and offers an efficient design principle for the methanol e-refinery reaction to formate, which may open up new research directions in understanding and designing electrified conversions of small molecules.

Highly Efficient and Stable Hydrogen Evolution from Natural Seawater by Boron-Doped Three-Dimensional Ni2P-MoO2 Heterostructure Microrod Arrays

The rational design of highly active and stable electrocatalysts toward the hydrogen evolution reaction (HER) is highly desirable but challenging in seawater electrolysis. Herein we propose a strategy of boron-doped three-dimensional Ni2P-MoO2 heterostructure microrod arrays that exhibit excellent catalytic activity for hydrogen evolution in both alkaline freshwater and seawater electrolytes. The incorporation of boron into Ni2P-MoO2 heterostructure microrod arrays could modulate the electronic properties, thereby accelerating the HER. Consequently, the B-Ni2P-MoO2 heterostructure microrod array electrocatalyst exhibits a superior catalyst activity for HER with low overpotentials of 155, 155, and 157 mV at a current density of 500 mA cm-2 in 1 M KOH, 1 M KOH + NaCl, and 1 M KOH + seawater, respectively. It also exhibits exceptional performance for HER in natural seawater with a low overpotential of 248 mV at 10 mA cm-2 and a long-lasting lifetime of over 100 h.

The facile synthesis of FeP/CoP confined in N, P co-doped carbon derived from MOFs for an efficient pH-universal hydrogen evolution reaction

Electrochemical hydrogen production is greatly limited by the low efficiency, high cost, and poor stability of electrocatalysts. Here, we report a facile one-step method to synthesize nitrogen, phosphorus co-doped carbon encapsulated FeP/CoP derived from dual metal-organic frameworks (FeP/CoP@NPC). Thanks to the synergistic effect of its unique composition and structure, the resultant FeP/CoP@NPC shows excellent catalytic HER performance with low potentials of 198, 286, and 339 mV to achieve a current density of 10 mA cm^-2 in acidic, neutral, and alkaline media along with remarkable long-time durability, respectively. More importantly, this work provides an efficient strategy for fabricating high-performance and stable pH-universal catalysts toward hydrogen generation.

The Scalable Solid-State Synthesis of a Ni5P4/Ni2P–FeNi Alloy Encapsulated into a Hierarchical Porous Carbon Framework for Efficient Oxygen Evolution Reactions

The exploration of high-performance and low-cost electrocatalysts towards the oxygen evolution reaction (OER) is essential for large-scale water/seawater splitting. Herein, we develop a strategy involving the in situ generation of a template and pore-former to encapsulate a Ni5P4/Ni2P heterojunction and dispersive FeNi alloy hybrid particles into a three-dimensional hierarchical porous graphitic carbon framework (labeled as Ni5P4/Ni2P–FeNi@C) via a room-temperature solid-state grinding and sodium-carbonate-assisted pyrolysis method. The synergistic effect of the components and the architecture provides a large surface area with a sufficient number of active sites and a hierarchical porous pathway for efficient electron transfer and mass diffusion. Furthermore, a graphitic carbon coating layer restrains the corrosion of alloy particles to boost the long-term durability of the catalyst. Consequently, the Ni5P4/Ni2P–FeNi@C catalyst exhibits extraordinary OER activity with a low overpotential of 242 mV (10 mA cm−2), outperforming the commercial RuO2 catalyst in 1 M KOH. Meanwhile, a scale-up of the Ni5P4/Ni2P–FeNi@C catalyst created by a ball-milling method displays a similar level of activity to the above grinding method. In 1 M KOH + seawater electrolyte, Ni5P4/Ni2P–FeNi@C also displays excellent stability; it can continuously operate for 160 h with a negligible potential increase of 2 mV. This work may provide a new avenue for facile mass production of an efficient electrocatalyst for water/seawater splitting and diverse other applications.

Updated Perceptions on Polymer-Based Enhanced Oil Recovery Toward High-Temperature High-Salinity Tolerance for Successful Field Applications in Carbonate Reservoirs

The aging of the existing reservoirs makes the hydrocarbon extraction shift toward newer reserves, and harsh conditioned carbonates, which possess high temperature and high salinity (HTHS). Conventional polymer-flooding fails in these HTHS carbonates, due to precipitation, viscosity loss, and polymer adsorption. Therefore, to counteract these challenges, novel polymer-based cEOR alternatives employ optimized polymers, polymer–surfactant, and alkali–surfactant–polymer solutions along with hybrid methods, which have shown a potential to target the residual or remaining oils in carbonates. Consequently, we investigate novel polymers, viz., ATBS, Scleroglucan, NVP-based polymers, and hydrophobic associative polymers, along with bio-polymers. These selected polymers have shown low shear sensitivity, low adsorption, and robust thermal/salinity tolerance. Additionally, adding an alkali-surfactant to polymer solution produces a synergy effect of improved mobility control, wettability alteration, and interfacial-tension reduction. Thus, enhancing the displacement and sweep efficiencies. Moreover, low-salinity water can precondition high-salinity reservoirs before polymer flooding (hybrid method), to decrease polymer adsorption and viscosity loss. Thus, this paper is a reference for novel polymers, and their hybrid techniques, to improve polymer-based cEOR field applications under HTHS conditions in carbonates. Additionally, the recommendations can assist in project designs with reasonable costs and minimal environmental impact. The implication of this work will aid in supplementing the oil and gas energy sector growth, making a positive contribution to the Middle Eastern economy.