Enhanced electrocatalytic efficiencies for water electrolysis and para-nitrophenol hydrogenation by self-supported nickel cobalt phosphide-nickel iron layered double hydroxide p-n junction

Self-supported copper-cobalt oxide hybrid electrode for bifunctionally electrocatalytic nitrate reduction and methanol oxidation reactions

Electrochemical nitrate reduction reaction (NO3RR) to ammonia (NH3) is a sustainable approach to upcycle nitrate (NO3-) pollutant, the further pairing of cathodic NO3RR with anodic methanol oxidation reaction (MOR) enables coproduction of NH3 and formate chemicals by electrolysis at enhanced energy efficiency. Bifunctional catalytic electrode for both reactions is crucial for achieving such a target. In view of the strong NO3- adsorption ability of copper (Cu) and the high active hydrogen adsorption ability of cobalt (Co) based compound, the catalyst composed of Cu and Co elements facilitates the deoxidation and complete hydrogenation of NO3- into NH3. In addition, the Cu- and Co-containing material is also possible catalyst or precatalyst for MOR. Herein, a self-supported Cu-cobalt oxide (CoO) hybrid onto nickel foam substrate, denoted as Cu-CoO/NF electrode, was fabricated by electrodeposition at negative potential. Due to the relaying effect of Cu and CoO components during NO3RR, the Cu-CoO/NF achieved a decent faradaic efficiency (FE) of 84 ± 4 % and an NH3 yield of 0.40 ± 0.02 mmol h-1 cm-2 at a high operation potential of -0.1 V. Moreover, the Cu-CoO/NF demonstrated high MOR property for formate production at significantly reduced potential (over 0.2 V) compared to the oxygen evolution reaction. The NO3RR-MOR coelectrolyser enabled coproduction of NH3 and formate at reduced energy consumption. This work provides a promising paradigm for pairwise production of valuable chemicals via rational design of catalytic electrode and construction of coelectrolysis system.

Constructing NiCo-hydroxide/Ni Mott-Schottky heterostructure electrocatalyst for enhanced alkaline hydrogen evolution reaction by inducing interfacial electron redistribution

Designing and developing inexpensive and efficient catalysts for alkaline hydrogen evolution reaction (HER) applications is essential for the advancement of renewable energy. However, the inadequate charge transfer and higher energy barriers in the alkaline HER process resulted in limited HER efficiency. Herein, a novel highly efficient Mott-Schottky heterostructure catalyst was synthesized by rationally combining metallic Ni and nickel-cobalt layered double hydroxide (NiCo-LDH). The work function difference between NiCo-LDH and metallic Ni naturally drives rapid electron transfer at the heterointerface, ultimately resulting in the formation of a built-in electric field at the NiCo-LDH/Ni heterointerface. The in-built electric field can induce electron redistribution at the heterointerface, thereby modifying the electronic structure of the catalyst. This accelerates electron transfer and optimizes the adsorption strength between the catalyst and the intermediates, leading to enhanced conductivity and reduced reaction energy barriers for the HER process. Notably, the indepth mechanism of the NiCo-LDH/Ni electrocatalyst in HER was analyzed by in situ Raman and Density-functional theory (DFT) calculations. The results demonstrated that the rapid dissociation of water, optimized electronic structure, and diminished reaction barriers contributed to the enhanced HER activity. Accordingly, the well-designed NiCo-LDH/Ni/NF exhibited a favorable performance for HER with an overpotential of only 93 mV at 10 mA cm-2 together with a desirable long-time durability for 100 h. This study provides new insights into enhancing the intrinsic catalytic activity of the catalyst by modulating its electronic structure and broadens the application of Mott-Schottky heterojunctions in the field of HER.

Co-doped NiFe carbonate hydroxide hydrate nanosheets with edge effect constructed from spent lithium-ion battery ternary cathodes for oxygen evolution reaction

The recycling of spent lithium-ion batteries (LIBs) has received increasing attention for environment and resource reclamation. Converting LIBs wastes into high-efficiency catalysts is a win-win strategy for realizing resource reclamation and addressing sustainable energy challenges. Herein, we developed a simple method to upcycle spent-LIBs cathode powder into Co-doped NiFe carbonate hydroxide hydrate (Co/NFCH-FF) as a low-cost and efficient oxygen evolution reaction (OER) electrocatalyst. The optimized Co/NFCH-FF electrode appears very competitive OER performances with low overpotentials of 201 and 249 mV at 10 and 100 mA cm-2, respectively, a small Tafel slope of 48.4 mV dec-1, and a high long-term stability. Moreover, we reveal that the existence of Co atoms leads to the formation of a crystalline/amorphous (c/a) interface at the Co/NFCH nanosheet edge, inducing the nanosheets possess a unique edge effect to enhance electric fields and accumulate hydroxide ions (OH-) at the edge during the OER process. Benefiting from edge effect, Co/NFCH-FF shows outstanding intrinsic activity. Furthermore, Co atoms as dopants stabilize the electronic structure of Co/NFCH-FF, enabling Co/NFCH-FF to exhibit excellent catalytic stability. This work provides an effective strategy for converting the end-life LIBs to high-performance multicomponent OER electrocatalysts and proposes new insights into the mechanism of enhanced catalytic activity of Co/NFCH.

Molybdenum, tungsten doped cobalt phosphides as efficient catalysts for coproduction of hydrogen and formate by glycerol electrolysis

H2 and formate are important energy carriers in fuel-cells and feedstocks in chemical industry. The hydrogen evolution reaction (HER) coupling with electro-oxidative cleavage of thermodynamically favorable polyols is a promising way to coproduce H2 and formate via electrochemical means, highly active catalysts for HER and electrooxidative cleavage of polycols are the key to achieve such a goal. Herein, molybdenum (Mo), tungsten (W) doped cobalt phosphides (Co2P) deposited onto nickel foam (NF) substrate, denoted as Mo-Co2P/NF and W-Co2P/NF, respectively, were investigated as catalytic electrodes for HER and electrochemical glycerol oxidation reaction (GOR) to yield H2 and formate. The W-Co2P/NF electrode exhibited low overpotential (η) of 113 mV to attain a current density (J) of -100 mA cm-2 for HER, while the Mo-Co2P/NF electrode demonstrated high GOR efficiency for selective production of formate. In situ Raman and infrared spectroscopic characterizations revealed that the evolved CoO2 from Co2P is the genuine catalytic sites for GOR. The asymmetric electrolyzer based on W-Co2P/NF cathode and Mo-Co2P/NF anode delivered a J = 100 mA cm-2 at 1.8 V voltage for glycerol electrolysis, which led to 18.2 % reduced electricity consumption relative to water electrolysis. This work highlights the potential of heteroelement doped phosphide in catalytic performances for HER and GOR, and opens up new avenue to coproduce more widespread commodity chemicals via gentle and sustainable electrocatalytic means.

Aqueous Electrocatalytic Reduction as a Low‐Carbon and Green Route for Chemical Synthesis and Environmental Remediation

The green electricity‐driven electrocatalytic reduction of organic compounds in aqueous solution has merged as a sustainable and green platform for organic electrosynthesis, upcycling of chemical waste, and environmental remediation. Compared with the thermocatalytic hydrogenation process, the electrocatalytic reduction of organic compounds uses water as a proton source, which enables its operation at ambient conditions with simplified reaction schemes and significantly reduces operation cost and energy consumption. Most studies have demonstrated the development of electrocatalysts to boost the current efficiency, conversion, and product selectivity of the electrocatalytic reduction processes. Still, little attention has been paid to the mechanism (e. g., electron/proton transfer route) and related energetics behind the electrocatalytic reduction process. This Concept overviews the recent development of the electrocatalytic reduction systems for environmental remediation, pollutant upcycling, and valorization of biomass‐derived chemicals. This Concept highlights the underlying mechanisms and aims to provide instructive guidance on designing efficient and selective electrocatalytic systems.