Defect-Engineered Co3 O4 @Nitrogen-Deficient Graphitic Carbon Nitride as an Efficient Bifunctional Electrocatalyst for High-Performance Metal-Air Batteries

Ruthenium single-atom doping-driven modulation of Co3O4 spinel tetrahedral site 3d-orbital occupancy in lithium-oxygen batteries

Metal single-atom catalysts have attracted widespread attention in the field of lithium-oxygen batteries due to their unique active sites, high catalytic selectivity, and near total atomic utilization efficiency. Isolated metal atoms not only serve as the active sites themselves, but also function as modulators, reversely regulating the surface electronic structure of the support to enhance its inherent electrocatalytic activities. Despite the potential of isolated metal atom-driven active sites, understanding the structure-activity relationship remains a challenge. In this study, we present a ruthenium single-atom doping-driven cost-effective and durable tricobalt tetroxide electrocatalyst with excellent oxygen electrode electrocatalytic activity. The lithium-oxygen battery with this catalyst as the oxygen electrode demonstrates high performance, achieving a capacity of up to 25 000 mA h g-1 and maintaining good stability over 400 cycles at a current density of 100 mA g-1. This improvement is attributed to the exquisite control of the morphology and structure of the discharge product, lithium peroxide. The aresults of physical characterization and theoretical calculations reveal that isolated ruthenium atoms bond with the tetrahedral cobalt site, resulting in spin polarization enhancement and rearrangement of d orbital energy levels in cobalt. This rearrangement reduces the dz2 orbital occupancy and promotes their transfer to the octahedral cobalt site, thereby enhancing its adsorption capacity for the oxygen-containing intermediates, and ultimately increasing the electrocatalytic activity of the oxygen evolution reaction. This work presents an innovative strategy to regulate the catalytic activity of metal oxides by introducing another metal single atom.

A Facile Design for Water-Oxidation Molecular Catalysts Precise Assembling on Photoanodes

Regulating the interfacial charge transfer behavior between cocatalysts and semiconductors remains a critical challenge for attaining efficient photoelectrochemical water oxidation reactions. Herein, using bismuth vanadate (BiVO4 ) photoanode as a model, it introduces an Au binding bridge as holes transfer channels onto the surfaces of BiVO4 , and the cyano-functionalized cobalt cubane (Co4 O4 ) molecules are preferentially immobilized on the Au bridge due to the strong adsorption of cyano groups with Au nanoparticles. This orchestrated arrangement facilitates the seamless transfer of photogenerated holes from BiVO4 to Co4 O4 molecules, forming an orderly charge transfer pathway connecting the light-absorbing layer to reactive sites. An exciting photocurrent density of 5.06 mA cm-2 at 1.23 V versus the reversible hydrogen electrode (3.4 times that of BiVO4 ) is obtained by the Co4 O4 @Au(A)/BiVO4 photoanode, where the surface charge recombination is almost completely suppressed accompanied by a surface charge transfer efficiency over 95%. This work represents a promising strategy for accelerating interfacial charge transfer and achieving efficient photoelectrochemical water oxidation reaction.

NiFeRu/C and Ru, Fe-Ni5P4/C as complementary electrocatalyst for highly efficient overall water splitting

Designing and fabricating highly competent and inexpensive electrocatalysts are highly desirable for application in electrocatalytic water splitting. In this study, we synthesized NiFeRu/C nanofibers and Ru, Fe dual-doped Ni5P4 (Ru, Fe-Ni5P4)/C nanofibers as complementary electrocatalysts for overall water splitting through electrospinning, carbonization, and phosphorization treatment, respectively. The NiFeRu/C nanofibers and Ru, Fe-Ni5P4/C nanofibers showed high hydrogen evolution reaction and oxygen evolution reaction activity, respectively, due to the presence of numerous exposed active sites and optimized adsorption capacity for the reaction intermediates contributed by the synergistic interaction among different metal components in the electrocatalysts. Hence, the assembled asymmetrical electrolytic cell effectively promoted overall water splitting, requiring a voltage of 1.569, 1.744, and 1.872 V to achieve a current density of 100, 500, and 1,000 mA cm-2, respectively, and it was better than Pt/C||IrO2. Additionally, the electrolytic cell could work at 500 mA cm-2 for 100 h without any noticeable deterioration in activity, which indicated that it was durable at high current density. In this study, we described a novel method for designing highly efficient electrocatalysts for overall water splitting.

Highly-Exposed Co-CoO Derived from Nanosized ZIF-67 on N-Doped Porous Carbon Foam as Efficient Electrocatalyst for Zinc-Air Battery

Non-precious-metal based electrocatalysts with highly-exposed and well-dispersed active sites are crucially needed to achieve superior electrocatalytic performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) toward zinc-air battery (ZAB). Herein, Co-CoO heterostructures derived from nanosized ZIF-67 are densely-exposed and strongly-immobilized onto N-doped porous carbon foam (NPCF) through a self-sacrificial pyrolysis strategy. Benefited from the high exposure of Co-CoO heterostructures and the favorable mass and electron transfer ability of NPCF, the Co-CoO/NPCF electrocatalyst exhibits remarkable performance for both ORR (E1/2  = 0.843 V vs RHE) and OER (Ej = 10 mA cm-2  = 1.586 V vs RHE). Further application of Co-CoO/NPCF as the air-cathode in rechargeable ZAB achieves superior performance for liquid-state ZAB (214.1 mW cm-2 and 600 cycles) and flexible all-solid-state ZAB (93.1 mW cm-2 and 140 cycles). Results from DFT calculations demonstrate that the electronic metal-support interactions between Co-CoO and NPCF via abundant C-Nx sites is favorable for electronic structure modulation, accounting for the remarkable performance.

Template-assisted Fabrication of O-doped CoP Microflowers with Optimal Electronic Modulation for Electrochemical Hydrogen Evolution

Exploring efficient, affordable and stable electrocatalyst toward hydrogen evolution reaction (HER) is of great scientific significance for the practical implementation of the water splitting. The heteroatom doping represents a serviceable strategy to further elevate the catalytic performance for a transition metal-based electrocatalyst because of the electronic regulation effect. Herein, a reliable self-sacrificial template-engaged approach is proposed to synthesize O-doped CoP (denoted as O-CoP) microflowers, which simultaneously considers the regualtion of electronic configuration via anion doping and sufficient exposure of active sites via nanostructure engineering. The suitable O incorporation content in CoP matrix could tremendously modify the electronic configuration, accelerate the charge transfer, promote the exposure of active sites, strengthen the electrical conductivity, and adjust the adsorption state of H*. Consequently, the optimized O-CoP microflowers with optimal O concentration display a remarkable HER property with a small overpotential of 125 mV to afford a current density of 10 mA cm-2 , a low Tafel slope of 68 mV dec-1 and long-term durability for 32 h under alkaline electrolyte, manifesting a considerable potential application for hydrogen production at large scale. The integration of anion incorporation and architecture engineering in this work will bring in a depth insight for the design of low-cost and effective electrocatalysts in energy conversion and storage systems.

Graphene-Encapsulated Bifunctional Catalysts with High Activity and Durability for Zn-Air Battery

Carbon-based electrocatalysts with both high activity and high stability are desirable for use in Zn-air batteries. However, the carbon corrosion reaction (CCR) is a critical obstacle in rechargeable Zn-air batteries. In this study, a cost-effective carbon-based novel material is reported with a high catalytic effect and good durability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), prepared via a simple graphitization process. In situ growth of graphene is utilized in a 3D-metal-coordinated hydrogel by introducing a catalytic lattice of transition metal alloys. Due to the direct growth of few-layer graphene on the metal alloy decorated 3d-carbon network, greatly reduced CCR is observed in a repetitive OER test. As a result, an efficient bifunctional electrocatalytic performance is achieved with a low ΔE value of 0.63 V and good electrochemical durability for 83 h at a current density of 10 mA cm^-2 in an alkaline media. Moreover, graphene-encapsulated transition metal alloys on the nitrogen-doped carbon supporter exhibit an excellent catalytic effect and good durability in a Zn-air battery system. This study suggests a straightforward way to overcome the CCR of carbon-based materials for an electrochemical catalyst with wide application in energy conversion and energy storage devices.

Toward highly efficient bifunctional electrocatalysts for zinc-air batteries: from theoretical prediction to a ternary FeCoNi design

3d Transition-metal nitrogen-carbon nanocomposites (T-N-C, T = Fe, Co, Ni, etc.) with highly active M-N_x sites have received much attention in the field of rechargeable zinc-air battery research. However, how to rationally dope metallic elements to decorate T-N-C catalysts and enhance their electrocatalytic performances remains unclear. Herein, we demonstrated that cobalt-doped Fe-rich catalysts are effective in improving ORR performances by density functional theory (DFT) calculations. On this basis, we reported a kind of novel bifunctional electrocatalyst of hollow nitrogen-doped carbon tubes with coexisting M-N-C single atoms and alloy nanoparticles (denoted Fe_xCo_yNi_z@hNCTs). Benefiting from the synergistic effect between different components, the as-prepared Fe₄Co₁Ni₂@hNCT catalyst exhibited a small overpotential difference of 0.75 V between an OER potential at 10 mA cm^-2 and an ORR half-wave potential, as well as an excellent zinc-air battery performance, when serving as the air cathode. This work provided a scalable design concept for multi-metal doping toward high-performance T-N-C electrocatalysts.

Self-Powered Thermoelectric Hydrogen Sensors Based on Low-Cost Bismuth Sulfide Thin Films: Quick Response at Room Temperature

Thermoelectric (TE)-based gas sensors have attracted significant attention due to their high selectivity, low power consumption, and minimum maintenance requirements. However, it is challenging to find low-cost, environmentally friendly materials and simple device fabrication processes for large-scale applications. Herein, we report self-powered thermoelectric hydrogen (TEH) sensors based on bismuth sulfide (Bi₂S₃) fabricated from a low-cost Bi₂S₃ TE layer and platinum (Pt) catalyst. When working at room temperature, the monomorphic-type TEH sensor obtained an output response signal of 42.2 μV with a response time of 17 s at a 3% hydrogen atmosphere. To further improve device performance, we connected the patterned Bi₂S₃ films in series to increase the Seebeck coefficient to -897 μV K^-1. For comparison, the resulting N tandem-type TEH sensor yielded a distinguished output voltage of 101.4 μV, which was greater than the monomorphic type by a factor of 2.4. Significantly, the response and recovery time of the N-tandem-type TEH sensor to 3% hydrogen were shortened to 14 and 15 s, respectively. This work provides a simple, environmentally friendly, and low-cost strategy for fabricating high-performance TEH sensors by applying low-cost Bi₂S₃ TE materials.