An electropolymerizable zinc porphyrin carrying eight entities of peripheral bithiophene, 4 was newly designed and synthesized. In this design, the bithiophene entities were separated by a biphenyl spacer to minimize ground state interactions perturbing porphyrin π-electronic structure. By multi-cyclic voltammetry, thin-films of 4 were formed on transparent FTO electrode and were characterized by optical, electrochemical and STM measurements. Further, the ability of zinc porphyrin in 4 to axially coordinate phenyl imidazole functionalized fullerene, C60Im both in solution and on the film interface was performed and characterized. Fluorescence quenching of zinc porphyrin both in solution and in the film was observed upon binding of C60Im. Femtosecond transient absorption studies revealed excited state charge separation for the dyad in solution wherein the measured rate of charge separation, kCS and charge recombination, kCR were found to be 2 x 1010 s−1 and 1.2 x 109 s−1, respectively. In contrast, transient absorption studies performed on the dyad in the film were suggestive of energy transfer with minimal contributions from electron transfer. The present study brings out the importance of modulating photochemical reactivity of donor-acceptor dyad in film as compared to that in solution. The electro- and photocatalytic reduction of molecular nitrogen to ammonia (nitrogen reduction reaction, NRR) is of broad interest as an environmentally- and energy-friendly alternative to the Haber–Bosch process for agricultural and emerging energy applications. Herein, we review our recent findings from collaborative electrochemistry/surface science/theoretical studies regarding transition metal oxides, oxynitrides and sulfides as NRR catalysts. We found that, for all metal oxides and oxynitrides specifically, there is no Mars–van Krevelen mechanism and that the reduction of lattice nitrogen and N2 to NH3 occurs by parallel reaction mechanisms at O-ligated metal sites without incorporation of N into the oxide lattice. Additionally, the results highlight the importance of both O-ligation and the importance of N in stabilizing the transition metal cation in an intermediate oxidation state, for effective N≡N bond activation. For transition metal sulfides, various exfoliation treatments are known to yield Sulfur vacancies and DFT calculations corroborate N2 binding to S-vacancies, with substantial π-backbonding to activate dinitrogen. Most of our NRR catalysts were selective to ammonia production without appreciable competing production of H2.

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The electrocatalytic nitrogen reduction reaction (NRR) is of considerable interest due to its potential for less energy intensive and environmentally friendly ammonia production which is critical for agricultural and clean energy applications. However, the selectivity of NRR compared to the hydrogen evolution reaction (HER) often poses challenges for various catalysts, including Earth-abundant transition metal oxynitrides like Ti, V, and Co. In this work, a comparative analysis of the selectivity of these three metal oxynitrides was conducted, each having different metal oxophilicities. A combination of electrochemical, surface characterizations and density functional theory (DFT) calculations were employed to directly assess NRR and HER activities under the same reaction conditions. Results show that cobalt oxynitrides exhibit NRR activity at pH 10, involving the electrochemical reduction of both lattice-bound nitrogen and dissolved N2, although more HER activity was observed. In contrast, vanadium oxynitride films displayed HER inactivity at pH 7 and 10 but demonstrated NRR activity at pH 7, while titanium oxynitrides were active at pH 3.2 but inactive under neutral and basic pH conditions. These comprehensive studies highlight substantial variations in HER and NRR selectivity based on transition metal oxophilicity/azaphilicity, indicating distinct mechanisms governing NRR and HER mechanisms.

Transition metal carbides (TMCs) are of increasing interest for catalytic processes. Their performance and stability under common oxidative conditions in catalytic reactions are crucial for several applications, including catalysis and electrochemical reactions. In this work, we report a detailed XPS study of the interactions of stoichiometric NbC and TaC surfaces with common oxidizing agents like O2 and H2O, which are important media in many chemical processes. Experimental results showed that NbC reacts with O2 to produce Nb sub-oxrides, while TaC is inert to O2 exposure. TaC surfaces are more sensitive to H2O vapor, with a greater surface oxidation and hydroxylation. Atmospheric oxidation of NbC and TaC was also studied, and results showed that both films oxidized yielding to the formation of Nb2O5 and Ta2O5, hydroxylated/ oxide carbon species, and some adventurous carbon build-up. TMCs are catalytically active in many reactions, especially those involving electrochemical nitrogen reduction reactions (NRR) to ammonia. Experimental and DFT calculations were used to provide insight on how carbide surface structures change electrochemically and how that evolution relates to NRR activity. Results showed that NbC has NRR activity at pH 3.2 after immersion in 0.3 M NaOH, leaving niobium suboxides. However, photoemission data showed that the Nb2O5 overlayer is restored after polarization to -1.3 V vs. Ag/AgCl, inhibiting NRR activity. TaC, on the other hand, is inactive for NRR at potentials more positive than -1.0 V, as NaOH treatment fails to remove the Ta2O5 surface layer induced by ambient exposure. The study also found that the formation and stabilization of intermediate oxidation states on the surface of transition metal ions are crucial for N≡N bond activation and NRR activity.

Printed circuit board manufacturing involves subtractive copper (Cu) etching where fine features are developed with a specific spatial resolution and etch profile of the Cu interconnects. A UV-Vis ATR metrology, to characterize the chemical transitions, has been developed to monitor the state of the bath by an in-situ measurement. This method provides a direct correlation of the Cu etch bath and was able to predict a 35% lower etch rate that was not predicted by the three current monitoring methods (ORP, specific gravity, and conductivity). Application of this UV-Vis ATR probe confirmed that two industrial etch baths, in identical working conditions, confirmed a difference in Cu2+ concentration by the difference of the near IR 860nm peak. The scope of this probe allowed chemically specific monitoring of the Cu etch bath to achieve a successful regeneration for repeated use. Interlayer dielectrics (ILDs) provide mechanical and electrical stability to the 3D electrical interconnects found in IC devices. It is particularly important that the structural support is created properly in the multilayered architecture to prevent the electrical cross signaling in short range distances. A combined multiple internal reflection and transmission FTIR has been employed for the characterization of silicon oxycarbonitride (SiOCN) films. These dielectric low-k films incorporate various functional groups bonded to silicon and require chemical bonding insight in the transformation and curing process. Distinct SiOx bonding patterns were differentiated, and the structure of the films can be predicted based on the amount of Si network and caged species. Further optimization of the FTIR analysis must minimize interference from moisture that can impact the judgement of peak heights. To accommodate this, a high-quality glove box was designed for dry air feedthrough to achieve a 95% moisture reduction during analysis, where less than 0.1 mAbs of moisture is detected in the spectra (without additional correction). The glove box allows for the rapid analysis of multiple sample throughput to outpace alternative characterization methods while retaining low spectral noise and a dry environment for 24/7 analysis. There is a great need to identify new catalysts that are suitable for tackling current economic demands, one of which is the nitrogen reduction reaction (NRR). The development of the surface enhanced infrared absorption spectroscopy (SEIRAS) has been applied to characterize the NRR mechanisms on the vanadium oxynitride electrocatalyst. Electrochemical measurements demonstrate NRR activity that is up to three times greater in the presence of N2 than the control Ar. FTIR operando suggests that a considerable number of intermediates were formed and continued to increase in absorbing value under an applied potential of -0.8 V vs Ag/AgCl. XPS results of the post-NRR film suggest a restricting of the film where vanadium oxynitride films are prone to instabilities under the possible MvK mechanism. After 90 minutes of NRR, the NH3 generated was approximately 0.01 ppm was calculated for through the salicylate colorimetric method. On-going efforts are focusing on optimizing the vanadium oxynitride film by the tuning of the oxynitride ratios and crystalline properties to promote the formation of V≡N: during the nitrogen reduction reaction.