Single-atom catalysts (SACs) have enormous significance in heterogeneous catalysis. However, understanding how SACs function at the molecular level remains a huge challenge. Here, we report a general approach to anchor Pt single-atom intercalated in layered double hydroxide (LDH) and decipher the alternating synergy between Pt single-atom and Ni₃Fe LDH support for overall water splitting. Aided with Tafel slope, interface species evolution and control experiments, operando electrochemical impedance spectroscopy (EIS) can distinguish interface charge transport and elementary reactions during hydrogen and oxygen evolution reactions (HER and OER). For HER, interlayer Pt single-atom vastly enhances electron transferability of LDH support, and Ni₃Fe LDH support accelerates water dissociation, thus resulting in a mixture of mechanisms (Heyrovsky–Volmer and Tafel–Volmer) in 1 M KOH. For OER, interlayer Pt single-atom not only prompts active phase transition from NiFe LDH to Ni^2+δFe^3+ζO_xH_y, but also optimizes OER intrinsic activity of Ni^2+δ–O–Fe^3+ζ in Ni^2+δFe^3+ζO_xH_y. Overall, we provide a referential paradigm for SACs synthesis strategy and unscrambling its alternating synergy.

Electrocatalytic urea synthesis emerged as the promising alternative of Haber–Bosch process and industrial urea synthetic protocol. Here, we report that a diatomic catalyst with bonded Fe–Ni pairs can significantly improve the efficiency of electrochemical urea synthesis. Compared with isolated diatomic and single-atom catalysts, the bonded Fe–Ni pairs act as the efficient sites for coordinated adsorption and activation of multiple reactants, enhancing the crucial C–N coupling thermodynamically and kinetically. The performance for urea synthesis up to an order of magnitude higher than those of single-atom and isolated diatomic electrocatalysts, a high urea yield rate of 20.2 mmol h⁻¹ g⁻¹ with corresponding Faradaic efficiency of 17.8% has been successfully achieved. A total Faradaic efficiency of about 100% for the formation of value-added urea, CO, and NH₃ was realized. This work presents an insight into synergistic catalysis towards sustainable urea synthesis via identifying and tailoring the atomic site configurations.

The trade-offs between photoelectrode efficiency and stability significantly hinder the practical application of silicon-based photoelectrochemical devices. Here, we report a facile approach to decouple the trade-offs of silicon-based photocathodes by employing crystalline TiO₂ with graded oxygen defects as protection layer. The crystalline protection layer provides high-density structure and enhances stability, and at the same time oxygen defects allow the carrier transport with low resistance as required for high efficiency. The silicon-based photocathode with black TiO₂ shows a limiting current density of ~35.3 mA cm⁻² and durability of over 100 h at 10 mA cm⁻² in 1.0 M NaOH electrolyte, while none of photoelectrochemical behavior is observed in crystalline TiO₂ protection layer. These findings have significant suggestions for further development of silicon-based, III–V compounds and other photoelectrodes and offer the possibility for achieving highly efficient and durable photoelectrochemical devices.