Wood-Structured Nanomaterials as Highly Efficient, Self-Standing Electrocatalysts for Water Splitting.

Electrocatalytic water splitting (EWS) driven by renewable energy is widely considered an environmentally friendly and sustainable approach for generating hydrogen (H2), an ideal energy carrier for the future. However, the efficiency and economic viability of large-scale water electrolysis depend on electrocatalysts that can efficiently accelerate the electrochemical reactions taking place at the two electrodes. Wood-derived nanomaterials are well-suited for serving as EWS catalysts because of their hierarchically porous structure with high surface area and low tortuosity, compositional tunability, cost-effectiveness, and self-standing integral electrode configuration. Here, recent advancements in the design and synthesis of wood-structured nanomaterials serving as advanced electrocatalysts for water splitting are summarized. First, the design principles and corresponding strategies toward highly effective wood-structured electrocatalysts (WSECs) are emphasized. Then, a comprehensive overview of current findings on WSECs, encompassing diverse structural designs and functionalities such as supported-metal nanoparticles (NPs), single-atom catalysts (SACs), metal compounds, and heterostructured electrocatalysts based on engineered wood hosts are presented. Subsequently, the application of these WSECs in various aspects of water splitting, including the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), overall water splitting (OWS), and hybrid water electrolysis (HWE) are explored. Finally, the prospects, challenges, and opportunities associated with the broad application of WSECs are briefly discussed. This review aims to provide a comprehensive understanding of the ongoing developments in water-splitting catalysts, along with outlining design principles for the future development of WSECs.

Hollow Nitrogen-Doped porous carbon spheres decorated with atomically dispersed Ni-N3 sites for efficient electrocatalytic CO2 reduction.

Hollow nitrogen-doped porous carbon spheres (HNCS) with plentiful coordination N sites, high surface area, and superior electrical conductivity are ideal catalyst supports due to their easily access of reactants to active sites and excellent stability. To date, nevertheless, little has been reported on HNCS as supports to metal-single-atomic sites for CO2 reduction (CO2R). Here we report our findings in preparation of nickel-single-atom catalysts anchored on HNCS (Ni SAC@HNCS) for highly efficient CO2R. The obtained Ni SAC@HNCS catalyst exhibits excellent activity and selectivity for the electrocatalytic CO2-to-CO conversion, achieving a Faradaic efficiency (FE) of 95.2% and a partial current density of 20.2 mA cm-2. When applied to a flow cell, the Ni SAC@HNCS delivers above 95% FECO over a wide potential range and a peak FECO of 99%. Further, there is no obvious degradation in FECO and the current for CO production during continuous electrocatalysis of 9 h, suggesting good stability of Ni SAC@HNCS.

Adjusting the valence band center of Co-Ni-bimetallic sulfides through lattice expansion and stacking faults triggered by strain engineering to boost oxygen evolution reaction.

Stress engineering can improve catalytic performance by straining the catalyst lattice. An electrocatalyst, Co3S4/Ni3S2-10%Mo@NC, was prepared with abundant lattice distortion to boost oxygen evolution reaction (OER). With the assistance of the intramolecular steric hindrance effect of metal-organic frameworks, slow dissolution by MoO42- of the Ni substrate and recrystallization of Ni2+ was observed in the process of Co(OH)F crystal growth with mild temperature and short time reaction. The lattice expansion and stacking faults created defects inside the Co3S4 crystal, improved the material conductivity, optimized the valence band electron distribution of the material, and promoted the rapid conversion of the reaction intermediates. The presence of reactive intermediates of the OER under catalytic conditions was investigated using operando Raman spectroscopy. The electrocatalysts exhibited super high performance, a current density of 10 mA cm-2 at an overpotential of 164 mV and 100 mA cm-2 at 223 mV, which were comparable to those of integrated RuO2. Our work for the first time demonstrates that the dissolution-recrystallization triggered by strain engineering is a good modulation approach to adjust the structure and surface activity of catalyst, suggesting promising industrial application.

Lattice distortion of crystalline-amorphous nickel molybdenum sulfide nanosheets for high-efficiency overall water splitting: libraries of lone pairs of electrons and in situ surface reconstitution.

Lattice distortion is an important way to improve the electrocatalytic performance and stability of two-dimensional transition metal materials (2d-TMSs). Herein, a lattice distortion nickel-molybdenum sulfide electrocatalyst on foam nickel (NiMoS4-12/NF) has been synthesized through a novel, simple, and effective crystalline-amorphous strategy. The electrocatalyst only requires 1.47 V to obtain 10 mA cm-2 for overall water splitting (OWS) and can function stably for 100 h at a current density of 100 mA cm-2, demonstrating an excellent electrocatalytic performance and stability. From the results of the transmission electron microscopy (TEM) and electron paramagnetic resonance spectroscopy (EPR), it can be seen that the (104) crystal lattice of NiMoS4-12 undergoes interface strain under the crystalline-amorphous state, resulting in rich sulfur defects caused by lattice distortion, which could improve the intrinsic catalytic activity of NiMoS4-12. According to the differential charge density analysis, around the sulfur defects, the Mo and Ni atoms with abundant lone pairs of electrons acted as libraries of lone pairs of electrons to enable an efficient hydrogen evolution reaction (HER). From the total density of states (TDOS) and the Gibbs free energy of hydrogen adsorption (ΔGH*), the libraries of lone pairs of electrons not only effectively optimized the distribution of the surface electron density of states at the Fermi level, but also reduced the ΔGH*, thereby improving the intrinsic HER electrocatalytic performance. The in situ Raman test results demonstrate that during the oxygen evolution reaction (OER), the surface of the nickel molybdenum sulfide was reconstructed, and highly active Ni-OOH was generated. From the calculated free energy diagrams, the Ni-OOH could optimize the reaction barrier of the rate-determining step (RDS) for the OER to enhance the slow oxygen evolution reaction kinetics. This work will contribute to the rational design of a 2d-TMSs electrocatalyst, as well as investigation of the catalytic mechanism.