Carbon Nanotube-Coupled Seaweed-like Cobalt Sulfide as a Dual-Functional Catalyst for Overall Water Splitting

Leaching-Reconstruction Engineering of Anions on Ferronickel Phosphate Promotes the Enhancement of the Oxygen Evolution Reaction

Electrochemical reconstruction typically generates powerful active sites for the oxygen evolution reaction (OER). However, engineering effective reconstruction strategies to manipulate the in situ formation of desired catalytically active surfaces, generate powerful active sites, and enhance their catalytic performance remains a challenge. Herein, leveraging the oxidation-potential-assisted precipitation etching, a heterostructure of NiFeOOH/NiFe phosphate was meticulously engineered to achieve highly efficient OER. During the electrochemical reconstruction, the leaching of inactive PO43- species in NiFe phosphate facilitates the exposure of more Ni and/or Fe species and creates more pores, thereby contributing to the formation of a NiFeOOH layer on the surface of NiFe phosphate. The resultant NiFeOOH/NiFe phosphate exhibits excellent OER activity with an overpotential of 205 mV at 50 mA cm-2 in an alkaline electrolyte. The theoretical calculations reveal that the heterostructure of NiFeOOH/NiFe phosphate weakens the thermodynamic barrier from *O to *OOH, thus enhancing the OER activity. The present proof-of-concept study introduces a leaching engineering approach to facilitate further exploration and development of highly efficient energy-related applications.

Synergistic Interfacial Effect of Ru/Co3O4 Heterojunctions for Boosting Overall Water Splitting

Low-cost bifunctional electrocatalysts capable of efficiently driving the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are needed for the growth of a green hydrogen economy. Herein, a Ru/Co3O4 heterojunction catalyst rich in oxygen vacancies (VO) and supported on carbon cloth (RCO-VO@CC) is prepared via a solid phase reaction (SPR) strategy. A RuO2/Co9S8@CC precursor (ROC@CC) is first prepared by loading Co9S8 nanosheets onto CC, following the addition of RuO2 nanoparticles (NPs). After the SPR process in an Ar atmosphere, Ru/Co3O4 heterojunctions with abundant VO are formed on the CC. The compositionally optimized RCO-VO@CC electrocatalyst with a Ru content of 0.55 wt.% exhibits very low overpotential values of 11 and 253 mV at 10 mA cm-2 for HER and OER, respectively, in 1 m KOH. Further, a low cell voltage of only 1.49 V is required to achieve a current density of 10 mA cm-2. Density functional theoretical calculations verify that the outstanding bifunctional electrocatalytic performance originates from synergistic charge transfer between Ru metal and VO-rich Co3O4. This work reports a novel approach toward a high-efficiency HER/OER electrocatalyst for energy storage and conversion.

Bismuth-Doped Carbon Dots Decorated Escherichia coli for Enhanced Hydrogen Production

Photosynthetic inorganic biohybrid systems (PBSs) combining an inorganic photosensitizer with intact living cells provide an innovative view for solar hydrogen production. However, typical whole-cell biohybrid systems often suffer from sluggish electron transfer kinetics during transmembrane diffusion, which severely limits the efficiency of solar hydrogen production. Here, a unique biohybrid system with a quantum yield of 8.42% was constructed by feeding bismuth-doped carbon dots (Bi@CDS) to Escherichia coli (E. coli). In this biohybrid system, Bi@CDS can enter the cells and transfer the electrons upon light irradiation, greatly reducing the energy loss and shortening the distance of electron transfer. More importantly, the photocatalytic hydrogen production of the E. coli-Bi@CDs biohybrid system reached up to 0.95 mmol within 3 h under light irradiation (420-780 nm, 2000 W m-2), which is 1.36 and 2.38 times higher than that in the E. coli-CDs biohybrid system and the E. coli system, respectively. In addition, the mechanism of enhanced hydrogen production was further explored. It was found that the accelerated decomposition of glucose, the accelerated production of pyruvate, the inhibition of lactic acid, and the increase of formic acid were the reasons for the increase of hydrogen production. This work provides a novel strategy for improving the hydrogen production in photosynthetic inorganic biohybrid systems.

Sulfur Vacancy-Engineered Co3S4/MoS2-Interfaced Nanosheet Array for Enhanced Alkaline Overall Water Splitting

Electrochemical water splitting, a crucial reaction for renewable energy storage, demands highly efficient and stable catalysts. Defect and interface engineering has been widely acknowledged to play a pivotal role in improving electrocatalytic performance. Herein, we demonstrate a facile strategy to construct sulfur vacancy (Sv)-engineered Co3S4/MoS2-interfaced nanosheet arrays to modulate the interface electronic structure in situ reduction with NaBH4. The abundant sulfur vacancies and well-arranged nanosheet arrays in Sv-Co3S4/MoS2 lead to pronounced electrocatalytic properties for hydrogen and oxygen evolution reactions (HER/OER) in an alkaline medium, with observed overpotentials of 156 and 209 mV at 10 mA cm-2, respectively. Additionally, as a bifunctional electrocatalyst, Sv-Co3S4/MoS2 requires a cell voltage of 1.67 V at 10 mA cm-2 for overall water splitting and exhibits long-term stability with activity sustained for more than 20 h. This study provides a novel approach to producing transition metal compound-interfaced electrocatalysts with rich vacancies under mild conditions, showcasing their potential for efficient water splitting applications.

Engineering multilayer catalytic interfaces with N, S co-regulation for high performance water splitting

The rational design of hierarchical nano-heterojunction electrocatalysts with efficient and durable water splitting performance is a hot research topic in the field of sustainable energy conversion. Herein, chemical vapor deposition methods are exploited to dope N and S elements in a core-shell structured Co₃O₄@NiMoO₄ with a layered structure (N, S-Co₃O₄@NiMoO₄/NF₄₀₀). The close contact between Co₃O₄ nanowires and N, S co-doped NiMoO₄ cubic arrays facilitates electron transfer. The electronic structure of Ni, Co and Mo atoms could be optimized to enhance their electrical conductivity by modulation of N and S atoms. At current densities of 10 and 200 mA cm^-2, N, S-Co₃O₄@NiMoO₄/NF₄₀₀ has an overpotential of 200, 300 and 71 160 mV for the oxygen evolution reaction and hydrogen evolution reaction, respectively. Its water splitting voltages are 1.45 V and 2 V at 10 and 200 mA cm^-2. In addition, N, S-Co₃O₄@NiMoO₄/NF₄₀₀ can operate stably for 100 h at a current density of 50 mA cm^-2. This work provides a new approach to designing bifunctional catalysts with hierarchical heterogeneous structures co-regulated by dual elements.