The theoretically predicted volcano plot for hydrogen production shows the best catalyst as the one that ensures that the hydrogen binding step is thermodynamically neutral. However, the experimental realization of this concept has suffered from the inherent surface heterogeneity of solid catalysts. It is even more challenging for molecular catalysts because of their complex chemical environment. Here, we report that the thermoneutral catalyst can be prepared by simple doping of a platinum atom into a molecule-like gold nanocluster. The catalytic activity of the resulting bimetallic nanocluster, PtAu24(SC6H13)18, for the hydrogen production is found to be significantly higher than reported catalysts. It is even better than the benchmarking platinum catalyst. The molecule-like bimetallic nanocluster represents a class of catalysts that bridge homogeneous and heterogeneous catalysis and may provide a platform for the discovery of finely optimized catalysts.

Copper electrocatalysts can reduce CO to hydrocarbons at high overpotentials. However, a mechanistic understanding of CO reduction on nanostructured Cu catalysts has been lacking. Herein we show that the structurally precise ligand-protected Cu-hydride nanoclusters, such as CuHL (L is a dithiophosphate ligand), offer unique selectivity for electrocatalytic CO reduction at low overpotentials. Our density functional theory (DFT) calculations predict that the presence of the negatively charged hydrides in the copper cluster plays a critical role in determining the selectivity of the reduction product, yielding HCOOH over CO with a lower overpotential. The HCOOH formation proceeds via the lattice-hydride mechanism: first, surface hydrides reduce CO to HCOOH product, and then the hydride vacancies are readily regenerated by the electrochemical proton reduction. DFT calculations further predict that hydrogen evolution is less competitive than HCOOH formation at the low overpotential. Confirming the predictions, electrochemical tests of CO reduction on the CuHL cluster demonstrate that HCOOH is indeed the main product at low overpotential, while H production dominates at higher overpotential. The unique selectivity afforded by the lattice-hydride mechanism opens the door for further fundamental and applied studies of electrocatalytic CO reduction by copper-hydride nanoclusters and other metal nanoclusters that contain hydrides.

This paper describes the effects of doped metals on hydrogen evolution reaction (HER) electrocatalyzed by atomically controlled MAu 24 and M 2 Au 36 nanoclusters, where M = Pt and Pd. HER performances, such as onset potential (E onset ), catalytic current density, and turnover frequency (TOF), are comparatively examined with respect to the doped metals. Doping Pt or Pd into gold nanoclusters not only changes the electrochemical redox potentials of nanoclusters but also considerably improves the HER activities. E onset is found to be controlled by the nanocluster's reduction potential matching the reduction potential of H + . The higher catalytic current and TOF are observed with the doped nanoclusters in the order of PtAu 24 > PdAu 24 > Au 25 . The same trend is observed with the Au 38 group (Pt 2 Au 36 > Pd 2 Au 36 > Au 38 ). Density functional theory calculations have revealed that the hydrogen adsorption free energy (ΔG H ) is significantly lowered by metal-doping in the order of Au 25 > PdAu 24 > PtAu 24 and Au 38 > Pd 2 Au 36 > Pt 2 Au 36 , indicating that hydrogen adsorption on the active site of nanocluster is thermodynamically favored by Pd-doping and further by Pt-doping. The doped metals, albeit buried in the core of the nanoclusters, have profound impact on their HER activities by altering their reduction potentials and hydrogen adsorption free energies.

Heteroatom doping is a powerful means to tune the optical and electronic properties of gold clusters at the atomic level. We herein report that doping a Au cluster with Pt and Pd atoms leads to core-doped [PtAu(SCH)] and [PdAu(SCH)], respectively. Voltammetric investigations show that these clusters exhibit drastically different electronic structures; whereas the HOMO-LUMO gap of [PtAu(SCH)] is found to be 0.95 V, that of [PdAu(SCH)] is drastically decreased to 0.26 V, suggesting Jahn-Teller distortion of the 12-electron cluster. Density functional investigations confirm that the HOMO-LUMO gap of the Pd-doped cluster is indeed reduced. Analysis of the optimized geometry for the 12-electron [PdAu(SCH)] reveals that the rod-like MAu core becomes more flattened upon Pd-doping. Reversible geometrical interconversion between [PtAu(SCH)] and [PtAu(SCH)] is clearly demonstrated by manipulating the oxidation state of the cluster.

Temperature-dependent and ultrafast transient absorption measurements were carried out to probe the optical properties and exciton relaxation dynamics in metal-doped (Pt and Hg) Au25 clusters. Optical absorption and electrochemistry results have shown that the Pt-doped cluster has a distinctly different HOMO–LUMO gap than that of Au25, while the gap did not change much for Hg-doped Au25. A decrease in temperature had resulted in much sharper absorption features as well as an increased number of absorption peaks, enhanced oscillator strength, and a shift in the energy maximum to higher energies for all metal-doped Au25 clusters. Interestingly, the peaks observed for Pt and Hg-doped clusters are very different from that of undoped Au25 cluster, suggesting that the altered structures play a crucial role on their optical properties. From the analysis of absorption peak shifts, higher phonon energies of 67 ± 8 meV were determined for Pt- and Hg-doped Au25 clusters when compared to 43 ± 6 meV for undoped Au25. The larger phonon energies suggest stronger coupling of core-gold and shell-gold and are explained by contraction of metal-doped clusters. Ultrafast transient absorption results have shown that Pt-doping lead to faster excited state relaxation, where more than 70% of the created electron–hole pairs recombine within 20 ps. However, Hg-doping and undoped Au25 relax to shell gold and recombination takes a much longer time. The results are consistent with energy gap law, where the smaller energy gap for PtAu24 led to faster exciton relaxation. An interesting correlation between the spin–orbit coupled transitions and bleach maximum was observed, which can be ascribed to exciton localization in Au12-icosahedron.