Electrochemical water splitting in acid has been emerging as a powerful, sustainable and green protocol to produce hydrogen gas sources. In this study, we propose a novel strategy to fabricate RuO_x clusters anchored on self-assembled SnO₂ cubic nanocages (RuO_x-SnO₂ composites), which is substantiated by a combination of spectroscopy and microscopy. The resulting RuO_x-SnO₂ composite catalysts exhibit boosting oxygen evolution reaction (OER) performance: A Tafel slope of 41.2 mV·dec⁻¹ and a low overpotential of 225 mV@10 mA·cm⁻² in a 0.5 M H₂SO₄ (pH=0) electrolyte are achieved, outperforming the state-of-art OER catalyst of commercial RuO₂ (com-RuO₂). Notably, RuO_x-SnO₂ gives an extraordinarily large mass activity of 6873.4 A·g_Ru⁻¹ at the overpotential of 270 mV, which is approximately 170 times higher than that of com-RuO₂ (40.2 A·g_Ru⁻¹). The RuO_x-SnO₂ exhibits a good durability for at least 100 h@50 mA·cm⁻² and > 500 h@10 mA·cm⁻² and a stability of 30 hours at 100 mA·cm⁻² in an assembled proton exchange membrane water electrolysis, indicating that the engineered microstructure possesses significant potential for practical applications. The high intrinsic OER performance is attributed to the increasing density of exposed catalytic sites by downsizing RuO_x clusters with abundant oxygen vacancies (Ov, 1.02×10⁻¹² spin·mg_cat.⁻¹ determined by electron paramagnetic resonance). Furthermore, a Ru5c-Ov dual-active site mechanism is proposed by density functional theory calculations, that is, the moderate surface migration between five-coordinated surface Ru site (Ru5c) and Ov makes the *O→*OOH rate-determining step feasible. Moreover, this strategy provides a novel route for enhancing acidic OER activity and highly encouraging for their future applications of ruthenium-based composite catalysts.

Size hierarchy is a distinct feature of nanogold-catalysts as it can strongly affect their performance in various reactions. We developed a simple method to generate Au_nS_m nanoclusters of different sizes by thermal treatment of an Au₁₄₄(PET)₆₀ (PET: phenylethanethiol) parent cluster. These clusters, deposited on activated carbon, exhibit excellent catalytic performance in the hydrochlorination of acetylene. In-situ ultraviolet laser dissociation high-resolution mass spectrometry of the parent cluster in the presence of acetylene revealed a remarkable cluster size-dependence of acetylene adsorption, which is a crucial step in the hydrochlorination. Systematic density functional theory calculations of the reaction pathways on the differently-sized clusters provide deeper insight into the cluster size dependence of the adsorption energies of the reactants and afforded a scaling relationship between the adsorption energy of acetylene and the co-adsorption energies of the reactants (C₂H₂ and HCl), which could enable a qualitative prediction of the optimal Au_nS_m cluster for the hydrochlorination of acetylene.

The two-dimensional layered double hydroxides (LDHs) and zero-dimensional metal clusters have emerged as promising nanomaterials in the field of sustainable water oxidation, which can also facilitate joint experimental and computational studies. In this study, the synthesis of Ni₆@LDH composites, comprising atomically precise Ni₆(MPA)₁₂ (MPA: mercaptopropionic acid) clusters embedded into LDH nanosheets via electrostatic interaction, represents a significant advancement in the development of nanomaterials for sustainable water oxidation. Ni₆@NiFe-LDH exhibits superior electrochemical performance in oxygen evolution reaction (OER), exhibiting OER overpotentials of 198 mV@10 mA·cm⁻² and 290 mV@100 mA·cm⁻² with a low Tafel slope of 29 mV·dec⁻¹. It surpasses the corresponding NiFe-LDH and commercial RuO₂ catalysts, primarily due to the synergistic interaction between Ni₆ clusters and LDHs. Interestingly, our combined experimental and computational approach reveals that the M-OOH_ads formation is the rate-determining step (RDS) for the Ni₆-based catalysts, differing from the RDS for NiFe-LDH itself (the M-O_ads formation). These efforts serve as an attempt to push forward the current research frontier to study structure–property relationships progressing from the micro-/nano-level to the precise atomic-level.