Rational design of single atom catalyst is critical for efficient sustainable energy conversion. However, the atomic-level control of active sites is essential for electrocatalytic materials in alkaline electrolyte. Moreover, well-defined surface structures lead to in-depth understanding of catalytic mechanisms. Herein, we report a single-atomic-site ruthenium stabilized on defective nickel-iron layered double hydroxide nanosheets (Ru1/D-NiFe LDH). Under precise regulation of local coordination environments of catalytically active sites and the existence of the defects, Ru1/D-NiFe LDH delivers an ultralow overpotential of 18 mV at 10 mA cm−2 for hydrogen evolution reaction, surpassing the commercial Pt/C catalyst. Density functional theory calculations reveal that Ru1/D-NiFe LDH optimizes the adsorption energies of intermediates for hydrogen evolution reaction and promotes the O–O coupling at a Ru–O active site for oxygen evolution reaction. The Ru1/D-NiFe LDH as an ideal model reveals superior water splitting performance with potential for the development of promising water-alkali electrocatalysts.

Rational design of the catalysts is impressive for sustainable energy conversion. However, there is a grand challenge to engineer active sites at the interface. Herein, hierarchical transition bimetal oxides/sulfides heterostructure arrays interacting two-dimensional MoOx/MoS2 nanosheets attached to one-dimensional NiOx/Ni3S2 nanorods were fabricated by oxidation/hydrogenation-induced surface reconfiguration strategy. The NiMoOx/NiMoS heterostructure array exhibits the overpotentials of 38 mV for hydrogen evolution and 186 mV for oxygen evolution at 10 mA cm−2, even surviving at a large current density of 500 mA cm−2 with long-term stability. Due to optimized adsorption energies and accelerated water splitting kinetics by theory calculations, the assembled two-electrode cell delivers the industrially relevant current densities of 500 and 1000 mA cm−2 at record low cell voltages of 1.60 and 1.66 V with excellent durability. This research provides a promising avenue to enhance the electrocatalytic performance of the catalysts by engineering interfacial active sites toward large-scale water splitting.

Electrochemical water splitting is recognized as a practical strategy for impelling the transformation of sustainable energy sources such as solar energy from electricity to clean hydrogen fuel. To actualize the large-scale hydrogen production, it is paramount to develop low-cost, earth-abundant, efficient, and stable electrocatalysts. Among those electrocatalysts, alternative architectural arrays grown on conductive substrates have been proven to be highly efficient toward water splitting due to large surface area, abundant active sites, and synergistic effects between the electrocatalysts and the substrates. Herein, the advancement of nanoarray architectures in electrocatalytic applications is reviewed. The categories of different nanoarrays and the reliable and versatile synthetic approaches of electrocatalysts are summarized. A unique emphasis is highlighted on the promising strategies to enhance the electrocatalytic activities and stability of architectural arrays by component manipulation, heterostructure regulation, and vacancy engineering. The intrinsic mechanism analysis of electronic structure optimization, intermediates' adsorption facilitation, and coordination environments' amelioration is also discussed with regard to theoretical simulation and in situ identification. Finally, the challenges and opportunities on the valuable directions and promising pathways of architectural arrays toward outstanding electrocatalytic performance are provided in the energy conversion field, facilitating the development of promising water splitting systems.

To achieve efficient conversion of renewable energy sources through water splitting, low-cost, earth-abundant, and robust electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are required. Herein, vertically aligned oxygenated-CoS2–MoS2 (O-CoMoS) heteronanosheets grown on flexible carbon fiber cloth as bifunctional electrocatalysts have been produced by use of the Anderson-type (NH4)4[CoIIMo6O24H6]·6H2O polyoxometalate as bimetal precursor. In comparison to different O-FeMoS, O-NiMoS, and MoS2 nanosheet arrays, the O-CoMoS heteronanosheet array exhibited low overpotentials of 97 and 272 mV to reach a current density of 10 mA cm–2 in alkaline solution for the HER and OER, respectively. Assembled as an electrolyzer for overall water splitting, O-CoMoS heteronanosheets as both the anode and cathode deliver a current density of 10 mA cm–2 at a quite low cell voltage of 1.6 V. This O-CoMoS architecture is highly advantageous for a disordered structure, exposure of active heterointerfaces, a “highway” of charge transport on two-dimensional conductive channels, and abundant active catalytic sites from the synergistic effect of the heterostructures, accomplishing a dramatically enhanced performance for the OER, HER, and overall water splitting. This work represents a feasible strategy to explore efficient and stable bifunctional bimetal sulfide electrocatalysts for renewable energy applications.

Solar carbon dioxide (CO 2 ) conversion is an emerging solution to meet the challenges of sustainable energy systems and environmental/climate concerns. However, the construction of isolated active sites not only influences catalytic activity but also limits the understanding of the structure−catalyst relationship of CO 2 reduction. Herein, we develop a universal synthetic protocol to fabricate different single-atom metal sites (e.g., Fe, Co, Ni, Zn, Cu, Mn, and Ru) anchored on the triazine-based covalent organic framework (SAS/Tr-COF) backbone with the bridging structure of metal−nitrogen−chlorine for highperformance catalytic CO 2 reduction. Remarkably, the as-synthesized Fe SAS/Tr-COF as a representative catalyst achieved an impressive CO generation rate as high as 980.3 μmol g −1 h −1 and a selectivity of 96.4%, over approximately 26 times higher than that of the pristine Tr-COF under visible light irradiation. From X-ray absorption fine structure analysis and density functional theory calculations, the superior photocatalytic performance is attributed to the synergic effect of atomically dispersed metal sites and Tr-COF host, decreasing the reaction energy barriers for the formation of *COOH intermediates and promoting CO 2 adsorption and activation as well as CO desorption. This work not only affords rational design of state-of-the-art catalysts at the molecular level but also provides in-depth insights for efficient CO 2 conversion.

Developing robust oxygen evolution reaction (OER) catalysts requires significant advances in material design and in-depth understanding for water electrolysis. Herein, we report iridium clusters stabilized surface reconstructed oxyhydroxides on amorphous metal borides array, achieving an ultralow overpotential of 178 mV at 10 mA cm À2 for OER in alkaline medium. The coupling of iridium clusters induced the formation of high valence cobalt species and Ir-O-Co bridge between iridium and oxyhydroxides at the atomic scale,engineering lattice oxygen activation and non-concerted proton-electron transfer to trigger multiple active sites for intrinsic pH-dependent OER activity.T he lattice oxygen oxidation mechanism (LOM) was confirmed by in situ 18 O isotope labeling mass spectrometry and chemical recognition of negative peroxo-like species.Theoretical simulations reveal that the OER performance on this catalyst is intrinsically dominated by LOM pathway,facilitating the reaction kinetics. This work not only paves an avenue for the rational design of electrocatalysts,b ut also serves the fundamental insights into the lattice oxygen participation for promising OER application.

No abstract

Direct photoelectrochemical (PEC) water splitting is a promising solution for solar energy conversion; however, there is a pressing bottleneck to address the intrinsic charge transport for the enhancement of PEC performance. Herein, a versatile coupling strategy was developed to engineer atomically dispersed Ni-N 4 sites coordinated with an axial direction oxygen atom (Ni-N 4 -O) incorporated between oxygen evolution cocatalyst (OEC) and semiconductor photoanode, boosting the photogenerated electron−hole separation and thus improving PEC activity. This state-ofthe-art OEC/Ni-N 4 -O/BiVO 4 photoanode exhibits a record high photocurrent density of 6.0 mA cm −2 at 1.23 V versus reversible hydrogen electrode (vs RHE), over approximately 3.97 times larger than that of BiVO 4 , achieving outstanding long-term photostability. From X-ray absorption fine structure analysis and density functional theory calculations, the enhanced PEC performance is attributed to the construction of single-atomic Ni-N 4 -O moiety in OEC/BiVO 4 , facilitating the holes transfer, decreasing the free energy barriers, and accelerating the reaction kinetics. This work enables us to develop an effective pathway to design and fabricate efficient and stable photoanodes for feasible PEC water splitting application.