{'fraction_non_alphanumeric': 0.03009660639088432, 'fraction_numerical': 0.018763933614069854, 'mean_word_length': 4.853207683943458, 'pattern_counts': {'":': 0, '<': 1, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Control over Electrochemical Water Oxidation Catalysis by Preorganization of Molecular Ruthenium Catalysts in Self‐Assembled Nanospheres

Abstract Oxygen formation through water oxidation catalysis is a key reaction in the context of fuel generation from renewable energies. The number of homogeneous catalysts that catalyze water oxidation at high rate with low overpotential is limited. Ruthenium complexes can be particularly active, especially if they facilitate a dinuclear pathway for oxygen bond formation step. A supramolecular encapsulation strategy is reported that involves preorganization of dilute solutions (10−5  m) of ruthenium complexes to yield high local catalyst concentrations (up to 0.54 m). The preorganization strategy enhances the water oxidation rate by two‐orders of magnitude to 125 s−1, as it facilitates the diffusion‐controlled rate‐limiting dinuclear coupling step. Moreover, it modulates reaction rates, enabling comprehensive elucidation of electrocatalytic reaction mechanisms.


Encapsulation studies by 1 H NMR
The encapsulation of various amounts of Ru complex inside the nanosphere was confirmed by 1 H NMR titration and 2D 1 H-DOSY NMR measurements. All experiments were performed in CD3CN at 298 K. For 1 H DOSY NMR measurements and the corresponding 1 H NMR measurements, 0.42 mM sphere solutions (10 mM based on the building block) were used and added the required amounts of guests (using stock solutions). In the presence of increasing amounts of guests, the typical shifts in the 1 H NMR are observed that indicate binding via hydrogen bonding to the guanidinum binding sites. 6 Also 1 H DOSY NMR confirms binding of the sulfonated ruthenium complexes in the guanidinum containing spheres. The spheres have a large size and accordingly small diffusion coefficient (D). The ruthenium complexes are much smaller and have significantly bigger D. In the 1 H DOSY NMR spectra of the mixture of sphere and ruthenium guests, only one band is observed for both the sphere and the guest at a logD value that is typical for the sphere. This experiment demonstrates that the guest is fully encapsulated in the spheres under these conditions. 6

Cold-spray-ionization time-of-flight mass spectrometry (CSI-ToF-MS) encapsulation studies
The molecular spheres in the presence and absence of Ru(bda)(PySO3TBA)2 were also analyzed by cold-spray-ionization time-of-flight mass spectrometry (CSI-ToF-MS) using a bruker IMPACT II. The MS spectra of the sphere were identical to those reported previously. 6 In the presence of Ru(bda)(PySO3TBA)2 no signals were detected, unless the TBA salt was removed first by dialysis. Peaks belonging to the nanosphere with 1 and 2 Ru(bda)(PySO3TBA)2 were observed.

Molecular modelling on the nanospheres
The initial model building was completed using an in-house developed automation script as illustrated in Fig. S13. This script assembles a nanosphere structure based on a crystal structure derived template using ProFit, 7 adds solvents, counter ions and guests using Packmol 8 and lastly conducts minimization and molecular dynamics simulation using the Amber15 software suite. 9 The guests were placed iteratively with implicit solvent molecular dynamics between each placement in order to obtain a reasonable starting structure. Afterwards acetonitrile, 10 water, 11 tetra-butyl ammonium and boron tetrafluoride ions 10 were added and enclosed in a 35 ångstrom periodic box. The atomic charges and Amber force field 8 parameters were specifically developed for the nanosphere ligands and metal centers using a combination of DFT calculations (um06l/def2TZVPP with scrf/smd implicit acetonitrile), executed using Gaussian 09 rev. D, 12 Merz-Kollman electrostatic potential charge fitting, completed using antechamber 13 , and genetic algorithm parameterization, using Paramfit. 14 Then five sequential 500 ps molecular dynamics simulations with constant pressure were used to equilibrate the solvent box, following this production molecular dynamics were run under constant volume with a Langevin thermostat and a low collusion frequency to accurately simulate Newtonian dynamics over a 5 ns trajectory. This procedure was completed for each nanosphere loading from 0 to 16 catalysts, with 7 replicates of each loading in order to account for variability due to initial packing. All molecular dynamics calculations were completed using pmemd. 15 CUDA and an Nvidia 980GTX general purpose graphics processor. The model, parameter, and input files used for this simulation are available upon request. The resulting trajectories were then analyzed using cpptraj 16 and visualized using VMD. 17 The nanosphere diffusion was calculated from the mean squared displacement of the nanosphere center of mass. Calculation of the individual catalyst displacement was calculated similarly, but after alignment of each trajectory frame to the nanosphere's palladium centers.
Radial distances were computed relative to the nanosphere center of mass to the individual palladium, guanidinium moiety and catalyst centers of mass.
The series of molecular dynamics calculations enabled analysis of preferential catalyst locations as function of the catalyst loading, by calculating the average distance from the center of the nanosphere (i.e. the centroid of the palladium centers).
Calculations for systems with up to 16 catalysts were performed, over the course of five trajectories (5 ns) sampled at 10 ps intervals, and the radial distribution plots are provided in Fig. S14 and the results are summarized in Fig. S15. In systems where 1-12 catalysts are present, the ruthenium complexes dominantly reside at the endohedral-bound region (6-15 Å) nearby the guanidinium moieties of the nanosphere, as a result of the hydrogen bond formation between the catalyst and guanidinium binding site. Only when more than 12 catalysts were present, the endohedral-free region (<6 Å), that is at the center of the nanosphere with limited opportunity for guanidinium interaction, and the pore region (15-20 Å) featuring catalysts with similar radial distributions as the palladium centers were occupied. Figure S15. The population of each binding region at catalyst loadings varying from 1 to 16 equivalents; endohedral free is at the core were hydrogen bonding with guanidinum units is impossible, endohedral bound is within the nanosphere at hydrogen bonding distance from the guanidinum units, and pore is at the same distance from the center as the palladium atoms at the periphery of the nanosphere.
The number of hydrogen bonds between the guanidinium moiety and each catalyst was counted individually by cpptraj, showing that at all loadings, each catalyst was on average bound with 3-4 bonds (Fig. S14). This varied significantly on both distance and loading, in general catalysts residing in the endohedral or pore regions included an average of 2 bonds, whereas those in the endohedral bound region were found with an average of 4. This average persisted in part due to the formation of bridging structures where guanidinium groups would bridge the sulfonates of two catalysts, in addition to the previously reported binding motifs (Fig. S16). These results indicate that catalysts are localized to favorable regions within the nanosphere environment dictated by the interaction with guanidinium moieties. The increased occupancy of less favorable regions (pore and endohedral free) is increased at higher loadings due to steric limitations of the catalysts. We infer that catalysts in the pore region are likely to be monotonically bound, and display a free sulfonate from the nanosphere surface, leading to aggregation and precipitation of the structure. This in turn limits the number of catalysts per sphere and dictates the stability of the system over longer time scales based on the occupancy of these pore sites.
The diffusion of the Ru(bda)(PySO3 -)2 within the nanosphere was calculated from the molecular dynamics simulations by calculating the mean square deviation of the trajectory aligned to the palladium centers. Fig. S17 shows the diffusion of the nanosphere as well as the diffusion of the catalyst guest within the sphere as function of the catalyst loading. The diffusion value for the nanosphere was calculated from the mean squared deviation of the nanosphere's center of mass over the course of each simulation, and at increased catalyst loading the diffusion is slightly lower. We attribute this to the increased solvent viscosity from the commiserate addition of BF4counter ions into the solvent upon addition of the ruthenium complexes. The diffusion of the catalysts within the cage environment was calculated from the same mean squared deviation, with the motion of the nanosphere removed by alignment of the trajectory frames to the palladium centers. We also see a similar small decrease in the Ru(bda)(PySO3 -)2 mobility indicating that the binding does not change the viscosity within the cage. Intuitively, if all catalyst are hydrogen bonded via 8 hydrogen bonds, one would expect a much more dramatic decrease in mobility.
Closer inspection of the data shows that at higher loadings, the catalysts are hydrogen bonded on average by 3-4 hydrogen bonds, as steric restrictions prevent the full number of hydrogen bonds to be formed. As a result, the system remains sufficiently dynamic to allow rapid diffusion for oxygen radical coupling reactions to occur.

Cyclic voltammetry measurements
Cyclic voltammetry (CV) measurements were recorded using a PG-STAT302N potentiostat with a three electrode system, glassy carbon working electrode, platinum coil counter electrode, and Ag/AgCl reference electrode, in acetonitrile containing 0.1 M TBAPF6 (tetrabutylammonium hexafluorophosphate) as supporting electrolyte and 10% water as substrate. The working electrode was polished and prior to use several CV scans were performed in electrolyte across a wide potential window to remove any adsorbed species left over from the polishing procedure prior to measurements. This was repeated until the scans overlap, and no peaks are observed. This process was repeated between measurements over the course of an experiment.   The solutions containing 0.02 mM Pt and Pd spheres overlap with the blank and no peaks nor current changes were observed after successive CV measurements, indicating good stability of the nanospheres under measurement conditions. Considering Pt sphere usually has better stability than Pd sphere, so we used Pt sphere to evaluate the electrochemical performance.      The current declined by ~10% resulting from the nanosphere or/and catalyst decay during 8000s electrolysis, it was still higher than in absence of sphere. The charge was calculated to be 0.29 C by integration of current and the turnover number (TON) was calculated to be around 1.5.
In order to further confirm the stability of the system and get a higher TON, bulk electrolysis was conducted with large surface area of foam carbon as working electrode (0.6 cm × 0.5 cm × 0.5 cm) under standard conditions at 1.3 V with 20 mL electrolyte (Fig. S27d). The current drops slightly and the charge passed was integrated to be 3.96 C, and TON was calculated to be 20.5 (see following calculation details).

Rotating ring-disk electrode experiments
Rotating ring-disk electrode (RRDE, glassy carbon electrode) experiments were performed with a Gamry Reference 600 potentiostat and a Gamry RDE710 rotating electrode setup. The reference and counter electrodes are the same as mentioned above. The solutions were degassed by bubbling nitrogen for 30 min prior to measurements. Iron ferricyanide was used to determine the collection efficiency of our glassy carbon-disc Pt-ring RRDE assembly. The current at the ring is 34 % of the disc current for all rotation rates.

kcat calculation 18
The diffusion co-efficient (D) was determined based on the Randles-Sevcik relation in equation (1), In equation (1), n is the number of electrons transferred, F is the Faraday constant, A is the area of the working electrode (0.2826 cm 2 ), [cat] is the concentration of the catalyst (mol L -1 ), R is the ideal gas constant, and T is the temperature. In the present study, ip values were taken from the one-electron redox process of Ru III /Ru II .
The dependence of the catalytic current (icat) on catalyst concentration could be described using equation (2), where ncat (= 4) is the number of electrons involved in water oxidation and kcat is the rate for water oxidation.

GHI = GHI [ ]J GHI
(2) The D can be calculated from the dependence of the ip on the square root of scan rates (√υ) based on equation (1). Then kcat can be determined by combining equation (2) The requirements to obtain kcat values using the equations above are as follows 19 : (1) ip and √υ should have a linear relationship to follow the Randles-Sevcik equation.
(2) The rate constant of the reaction should be first-order to the concentration of the catalyst.
(3) icat should be independent to scan rates to obtain a purely kinetic conditions.
(4) The amount of the substrate should be large enough to obtain a kcat value as a pseudo first-order rate constant.
The requirements were fully confirmed by following experiments: (1) A linear relationship of ip and √υ confirmed: For the catalyst both in the presence and absence of sphere, the comparison of scan-rate-normalized CVs show a constant redox current of Ru III /Ru II at the scan rate of 10 to 1000 mV s -1 (Fig. S31) and a linear relation of ip and √υ was confirmed in Fig. S23, showing that the redox events take place in solution, not on adsorbed species. The redox currents of Ru III /Ru II can be used to calculate D. (2) Determination of a rate law: For the catalyst both in the presence and absence of sphere, the comparison of scan-rate-normalized CVs (icat/√υ) at υ from 10 to 1000 mV s -1 show a decrease in catalytic current (icat) with increased scan rate (Fig. S31), which is consistent with a contribution to the current from a rate-limiting water oxidation catalysis. icat values exhibit a linear relationship with sphere catalyst concentration (Fig. S26), indicating that the rate law for O2 evolution can be expressed by using equation 2.
(3) icat independent to scan rates confirmed: icat was measured at various scan rate from 10 to 1000 mV s -1 . As shown in Fig. S32, icat is independent to scan rate under measurement conditions. (4) icat independent to water concentration confirmed: icat was obtained with various water concentration at scan rate of 10 mV s -1 . As shown in Fig. S33, when the concentration of water is higher than 8%, the current is no longer dependent on the water concentration. kcat calculation by following procedures: As all the requirements were confirmed, the calculation can be conducted. As shown in Fig. S23, the slopes of the dependence of ip and √υ with sphere and without sphere were determined to be 6.9 and 16.3, respectively. Then D was calculated to be 2.87×10 -6 and 5.28×10 -7 cm 2 s -1 based on equation 1.
For kcat without sphere, as shown in Fig. S34, the plot of icat/ip against 1/√υ shows a linear relationship and the slope was found to be 1.36. The kcat value was determined to be 0.93 s -1 using equation 3.
With D and kcat without sphere in hand, the kcat of in the presence of sphere can be calculated based on equation 4.   nanosphere under standard conditions. The redox peak at 1.04 V is from Ru III/II of Ru(phenda)(PySO3 -)2, which is inactive to water oxidation in absence and presence the nanosphere in the measured potential window because of its large overpotential (Fig. S38). (b) CV measurements for 6 Ru(bda)(PySO3 -)2 (red) and 6 Ru(bda)(PySO3 -)2 + 6 Ru(phenda)(PySO3 -)2 (blue) were co-encapsulated in a nanosphere under standard conditions. Figure S38. CV measurements of Ru(phenda)(PySO3 -)2 without sphere (red) and with 4 (blue), 8 (yellow) and 12 (green) of Ru(phenda)(PySO3 -)2 per sphere under standard conditions. The catalytic performance was not enhanced because of the WNA mechanism, lower currents result from slower mobility of encapsulation to the nanosphere.