Surface engineered CoP/Co3O4 heterojunction for high-performance bi-functional water splitting electro-catalysis

Designing TiO2 Nanotubular Arrays with Au-CoOx Core-Shell Nanoparticles for Enhanced Photoelectrochemical Methanol and Lignin Oxidation

One-dimensional (1D) ordered TiO2 nanotubes exhibit exceptional charge transfer capabilities, making them suitable candidates for constructing visible-light-active photoanodes in selective PEC oxidation reactions. Herein, we employed a facile and easily scalable electrochemical method to fabricate Au-CoOx-deposited ordered TiO2 nanotubular array photoanodes. The improved visible light absorption capacity of TiO2-Au-CoOx, with unhampered 1D channels and the controlled integration of Au between TiO2 and CoOx, along with their synergistic interaction, have been identified as the most promising strategy for enhanced PEC performance, as evidenced by an IPCE of 3.7% at 450 nm. Furthermore, the robust interfacial charge transfer pathway from CoOx to the TiO2 surface via the Au mediator promotes the migration of photogenerated electrons and enables the accumulation of holes on the surface of CoOx. These holes are then efficiently utilized by oxidants such as methanol or lignin to generate value-added products, highlighting the potential of this system for advanced PEC applications.

Advancing Energy Sustainability Through Solar-to-Fuel Technologies: From Materials to Devices and Systems

To achieve carbon neutrality and sustainable development, innovative solar-to-fuel systems have been designed through the integration of solar energy harvesting and electrochemical devices. Over the last decade, there have been notable advancements in enhancing the efficiency and durability of these solar-to-fuel systems. Despite the advancements, there remains significant potential for further improvements in the performance of systems. Enhancements can be achieved by optimizing electrochemical catalysts, advancing the manufacturing technologies of photovoltaics and electrochemical cells, and refining the overall design of these systems. In the realm of catalyst optimization, the effectiveness of materials can be significantly improved through active site engineering and strategic use of functional groups. Similarly, the performance of electrochemical devices can be enhanced by incorporating specific additives into electrolytes and optimizing gas diffusion electrodes. Improvements in solar harvesting devices are achievable through efficient passivant and self-assembled monolayers, which enhance the overall quality and efficiency of these systems. Additionally, optimizing the energy conversion efficiency involves the strategic use of DC converters, photoelectrodes, and redox media. This review aims to provide a comprehensive overview of the advancements in solar-powered electrochemical energy conversion systems, laying a solid foundation for future research and development in the field of energy sustainability.

Engineering P-Fe2O3-CoP nanosheets for overall freshwater and seawater splitting

Tailoring surface composition and coordinative environment of catalysts in a nano-meter region often influence their chemical performance. It is reported that CoP exhibits a low dissociation ability of H-OH, originating from the poor desorption of intermediate species. Herein, we provide a feasible method to construct P-Fe2O3-CoP nanosheets through a gas-phase phosphorization process. P doping induces the formation of interfacial structure between Fe2O3 and CoP and the generation of defective structures. The resulting P-Fe2O3-CoP nanosheets afford high freshwater/seawater oxidation activity (250/270 mV@10 mA/cm2) in 1 mol/L (M) KOH, which is even lower than commercial RuO2. Compared with CoP||CoP, P-Fe2O3||P-Fe2O3, and Co3O4||Co3O4, the assembled P-Fe2O3-CoP||P-Fe2O3-CoP exhibits the superior water/seawater electrolysis performance with 1.61/1.65 V@10 mA/cm2. The synergistic effect of P doping, defective structure, and heterojunction leads to high water oxidation efficiency and water splitting efficiency.

Boosting catalytic activity toward methanol oxidation reaction for platinum via heterostructure engineering

Direct methanol fuel cell (DMFC) is hampered by the sluggish methanol oxidation reaction. In this work, we have invited rhodium phosphides (Rh2P) to platinum (Pt) as robust MOR electrocatalyst ascribing the excellent water dissociation capability of Rh2P to generate Pt(OH)ads species to mitigate the CO poisoning. MOR mass activity of Rh2P-Pt/C is enhanced by 2- and 3.5-time with relative to commercial Pt/C and PtRu/C, respectively; additionally, the CO anti-poisoning ability is also boosted by 2.4 folds than Pt/C. The in-situ electrochemical impedance spectroscopy test reveals that the water dissociation is accelerated by Rh2P; moreover, the mutual electronic interplay between Pt and Rh2P contributes to a superior resistance towards electrochemical dissolution and coalescence. The theoretical investigation also indicates that d band center of Pt in Rh2P-Pt is downshifted resulting in a lower CO binding strength.

In Situ Formation of CoP/Co3 O4 Heterojunction for Efficient Overall Water Splitting

Electrochemical water splitting is an environmentally friendly and effective energy storage method. However, it is still a huge challenge to prepare non-noble metal based electrocatalysts that possess high activity and long-term durability to realize efficient water splitting. Here, we present a novel method of low-temperature phosphating for preparing CoP/Co3 O4 heterojunction nanowires catalyst on titanium mesh (TM) substrate that can be used for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting. CoP/Co3 O4 @TM heterojunction showed an excellent catalytic performance and long-term durability in 1.0 M KOH electrolyte. The overpotential of CoP/Co3 O4 @TM heterojunction was only 257 mV at 20 mA cm-2 during the OER process, and it could work stably more than 40 h at 1.52 V versus reversible hydrogen electrode (vs. RHE). During the HER process, the overpotential of CoP/Co3 O4 @TM heterojunction was only 98 mV at -10 mA cm-2 . More importantly, when used as anodic and cathodic electrocatalyst, they achieved 10 mA cm-2 at 1.59 V. The Faradaic efficiencies of OER and HER were 98.4 % and 99.4 %, respectively, outperforming Ru/Ir-based noble metal electrocatalysts and other non-noble metal electrocatalysts for overall water splitting.

Molecular Engineering of Metal-Organic Frameworks as Efficient Electrochemical Catalysts for Water Oxidation

Metal-organic framework (MOF) solids with their variable functionalities are relevant for energy conversion technologies. However, the development of electroactive and stable MOFs for electrocatalysis still faces challenges. Here, a molecularly engineered MOF system featuring a 2D coordination network based on mercaptan-metal links (e.g., nickel, as for Ni(DMBD)-MOF) is designed. The crystal structure is solved from microcrystals by a continuous-rotation electron diffraction (cRED) technique. Computational results indicate a metallic electronic structure of Ni(DMBD)-MOF due to the Ni-S coordination, highlighting the effective design of the thiol ligand for enhancing electroconductivity. Additionally, both experimental and theoretical studies indicate that (DMBD)-MOF offers advantages in the electrocatalytic oxygen evolution reaction (OER) over non-thiol (e.g., 1,4-benzene dicarboxylic acid) analog (BDC)-MOF, because it poses fewer energy barriers during the rate-limiting *O intermediate formation step. Iron-substituted NiFe(DMBD)-MOF achieves a current density of 100 mA cm^-2 at a small overpotential of 280 mV, indicating a new MOF platform for efficient OER catalysis.

Revealing the influence of conversion-type Co3O4 dimensionality on cyclic and rate performance for lithium storage

Cobalt tetraoxide (Co₃O₄) is regarded as a promising anode material for Li-ion batteries owing to its high theoretical capacity (890 mAh g^-1), simple preparation, and controllable morphology. Nanoengineering has been proven to be an effective method for producing high-performance electrode materials. However, systematic research on the influence of material dimensionality on battery performance is lacking. Herein, we prepared Co₃O₄ with various dimensionalities (one-dimensional (1D) Co₃O₄ nanorod (NR), two-dimensional (2D) Co₃O₄ nanosheet (NS), three-dimensional (3D) Co₃O₄ nanocluster (NC), and 3D Co₃O₄ nanoflower (NF)) using a simple solvothermal heat treatment method, and their morphologies were controlled by varying the precipitator type and solvent composition. The 1D Co₃O₄ NR and 3D samples (3D Co₃O₄ NC and 3D Co₃O₄ NF) exhibited poor cyclic and rate performances, respectively, while the 2D Co₃O₄ NS exhibited the best electrochemical performance. The mechanism analysis revealed that the cyclic stability and rate performance of the Co₃O₄ nanostructures are closely related to their intrinsic stability and interfacial contact performance, respectively, and the 2D thin-sheet structure can achieve an optimal balance between the two, resulting in the best performance. This work presents a comprehensive study on the effect of dimensionality on the electrochemical performance of Co₃O₄ anodes, providing a new concept for the nanostructure design of conversion-type materials.

In Situ Construction of Heterostructured Co3O4/CoP Nanoflake Arrays on Carbon Cloth as Binder-Free Anode for High-Performance Lithium-Ion Batteries

Cobalt oxide (Co₃O₄) is regarded as the anode material for lithium-ion batteries (LIBs) with great research value owing to its environmental friendliness and exceptional theoretical capacity. However, the low intrinsic conductivity, poor electrochemical kinetics, and unsatisfactory cycling performance severely limit its practical applications in LIBs. The construction of a self-standing electrode with heterostructure by introducing a highly conductive cobalt-based compound is an effective strategy to solve the above issues. Herein, Co₃O₄/CoP nanoflake arrays (NFAs) with heterostructure are constructed skillfully directly grown on carbon cloth (CC) by in situ phosphorization as an anode for LIBs. Density functional theory simulation results demonstrate that the construction of heterostructure greatly increases the electronic conductivity and Li ion adsorption energy. The Co₃O₄/CoP NFAs/CC exhibited an extraordinary capacity (1490.7 mA h g^-l at 0.1 A g^-l) and excellent performance at high current density (769.1 mA h g^-l at 2.0 A g^-l), as well as remarkable cyclic stability (451.3 mA h g^-l after 300 cycles with a 58.7% capacity retention rate). The reasonable construction of heterostructure can promote the interfacial ion transport, significantly enhance the adsorption energy of lithium ions, improve the conductivity of Co₃O₄ electrode material, promote the partial charge transfer throughout the charge and discharge cycles, and enhance the overall electrochemical performance of the material.

Boosting Hydrogen Evolution Electrocatalysis via Regulating the Electronic Structure in a Crystalline-Amorphous CoP/CeOx p-n Heterojunction

The modulation of the electronic structure is the effective access to achieve highly active electrocatalysts for the hydrogen evolution reaction (HER). Transition-metal phosphide-based heterostructures are very promising in enhancing HER performance but the facile fabrication and an in-depth study of the catalytic mechanisms still remain a challenge. In this work, the catalytically inactive n-type CeOx is successfully combined with p-type CoP to form the CoP/CeOx heterojunction. The crystalline-amorphous CoP/CeOx heterojunction is fabricated by the phosphorization of predesigned Co(OH)2/CeOx via the as-developed reduction-hydrolysis strategy. The p-n CoP/CeOx heterojunction with a strong built-in potential of 1.38 V enables the regulation of the electronic structure of active CoP within the space-charge region to enhance its intrinsic activity and facilitate the electron transfer. The functional CeOx entity and the negatively charged CoP can promote the water dissociation and optimize H adsorption, synergistically boosting the electrocatalytic HER output. As expected, the heterostructured CoP/CeOx-20:1 with the optimal ratio of Co/Ce shows significantly improved HER activity and favorable kinetics (overpotential of 118 mV at a current density of 10 mA cm-2 and Tafel slope of 77.26 mV dec-1). The present study may provide new insight into the integration of crystalline and amorphous entities into the p-n heterojunction as a highly efficient electrocatalyst for energy storage and conversion.

Freestanding 2D NiFe Metal-Organic Framework Nanosheets: Facilitating Proton Transfer via Organic Ligands for Efficient Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is crucial to electrochemical hydrogen production. However, designing and fabricating efficient electrocatalysts still remains challenging. By confinedly coordinating organic ligands with metal species in layered double hydroxides (LDHs), an innovative LDHs-assisted approach is developed to facilely synthesize freestanding bimetallic 2D metal-organic framework nanosheets (2D MOF NSs), preserving the metallic components and activities in OER. Furthermore, the research has demonstrated that the incorporation of carboxyl organic ligands coordinated with metal atoms as proton transfer mediators endow 2D MOF NSs with efficient proton transfer during the electrochemical OH_ads  → O_ads transition. These freestanding NiFe-2D MOF NSs require a small overpotential of 260 mV for a current density of 10 mA cm^-2 . When this strategy is applied to LDH nanosheets grown on nickel foam, the overpotential can be reduced to 221 mV. This outstanding OER activity supports the capability of multimetallic organic frameworks for the rational design of water oxidation electrocatalysts. This strategy provides a universal path to the synthesis of 2D MOF NSs that can be used as electrocatalysts directly.