We report the stepwise in-situ manipulation of a nickel cubane nanocluster capped with a specially designed multidentate ligand [Ni^II₄(HL)₃(CH₃O)(CH₃OH)₃](CH₃COO) (Ni4, H₃L = (E)-3-((2-hydroxy-3-methoxybenzylidene)amino)propane-1,2-diol) to firstly [Ni^II₄(HL)₃(CH₃O)(CH₃OH)₂(H₂O)](CH₃COO) (Ni4-1min) and finally to [Ni^II₄(HL)₃ (CH₃O)(H₂O)₃](CH₃COO) (Ni4-20h) during the urea electrolysis. A combination of mass spectrometry, single crystallography and Pair Distribution Function were employed to analyze the structural correlations of this catalyst in crystal/solution/gas phases for confirming the dynamic ligand replacement while preserving the cubic Ni4 core during catalysis. The key feature of their structures is that: i) three ligands wrap the Ni4O4 cubane center on one side forming the rounded outside of a calix; ii) the opposite flat side containing labile methanol as the active site. This structure facilitates the binding of the substrate to the active central nickel atoms during catalysis. Furthermore, due to the different modes of packing, the structure of Ni4-20h sustains 2D net of open space while the structures of Ni4 and Ni4-1min have only closed void inaccessible to solvent molecules or ions. Interestingly, the overpotential initially decreased (up to 45 minutes) until it is stabilized. The result showed a low potential of 1.32 V (UOR) at 10 mA cm^–2 as reflected in the Gibbs free energy decrease of ~0.4 eV from Ni4 to Ni4-20h. This work demonstrates a convincing approach for elucidating the exact nature of the active clusters in electrocatalytic process, and confirms that in-situ modification of electrode materials might alter the direct electronic interaction between substrate and active sites in improving the catalytic performance.

The development of novel single-atom catalysts is important for highly efficient electrochemical catalysis and sensing. In this work, a novel Pt single atoms (SAs) supported on Ni₆Co₁ layered double hydroxides/nitrogen-doped graphene (Pt₁/Ni₆Co₁LDHs/NG) was constructed for electrochemical enzyme-free catalysis and sensing towards glucose. The loading of Pt single atoms increases with doping of Co atoms that generate more anchoring sites for Pt SAs. The resulting Pt₁/Ni₆Co₁LDHs/NG exhibits low oxidative potential of 0.440 V with high sensitivity of 273.78 μA·mM⁻¹·cm⁻² toward glucose, which are 85 mV lower and 15 times higher than those of Ni(OH)₂, respectively. Pt₁/Ni₆Co₁LDHs/NG also shows excellent selectivity and great stability during 5-week testing. Theoretical and experimental results show that the boosted performance of Pt₁/Ni₆Co₁LDHs/NG originates from its stronger binding energy with glucose and the synergistic effect of Pt SAs, Co doping, and NG. This work provides a general strategy of designing highly active SACs for extending their application in electrochemical sensing.