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The electrochemical properties of $\beta$-octaethylporphycene iridium complex (Ir-OEPo) were determined. Based on the electro-spectro measurement results, the reduction of Ir-OEPo did not occur at the central metal but at the ligand, while the reduction of $\beta$-octaethylporphyrin iridium complex (Ir-OEPor) occurred at the central iridium. A catalytic current was observed during the cyclic voltammetry (CV) measurements with trifluoroacetic acid (TFA) under a reductive condition, indicating the catalytic reactivity of Ir-OEPo for the hydrogen evolution reaction (HER). By constant potential electrolysis, hydrogen gas was detected by gas chromatography (GC) and the catalytic reactivity of Ir-OEPo was confirmed. The HER mechanism via ligand reduction of macrocyclic aromatic complexes could be one of the concepts for the development of new catalysts.

Photoelectrochemical proton reduction for H₂ production was found with zinc tetraphenylporphin (ZnTPP) dispersed into a poly(4-vinylpyridine) (PVP) membrane coated on a platinum electrode (Pt/PVP[ZnTPP]) and dipped in an aqueous solution. The photocurrent in the Pt/PVP[ZnTPP] system was generated in the potential region below −0.40 V (vs. Ag/AgCl). The action spectrum of the photocurrent showed that the photoelectrochemical event is induced by the excitation of ZnTPP. The singlet lifetime of the PVP[ZnTPP] system under the applied potential of −0.45 V (vs. Ag/AgCl) is shorter than that without the applied potentials, showing that the singlet ZnTPP* species is quenched reductively to ZnTPP⁻ by electron injection from the platinum electrode. The proton is catalytically reduced to H₂ by ZnTPP⁻ supposedly on the platinum surface.

The splitting of water into its constituent elements is an important solar fuels conversion reaction for the storage of renewable energy. For each of the half reactions of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), multiple protons and electrons must be coupled to avoid high-energy intermediates. To understand the mechanistic details of the PCET chemistry that underpins HER and OER, we have designed hangman porphyrin and corrole catalysts. In these hangman constructs, a pendant acid/base functionality within the secondary coordination sphere is "hung" above the macrocyclic redox platform on which substrate binds. The two critical thermodynamic properties of a PCET event, the redox potential and pK_a may be tuned with the macrocycle and hanging group, respectively. This review outlines the synthesis of these catalysts, as well as the examination of the PCET kinetics of hydrogen and oxygen evolution by the hangman catalysts. The insights provided by these systems provide a guide for the design of future HER and OER catalysts that use a secondary coordination sphere to manage PCET.

Herein, we report photochemical hydrogen evolution systems consisting of various rhodium based catalysts with Wilkinson type structures, Zn metalated porphyrins and fluorescein as photosensitizers and triethanolamine as a sacrificial electron donor in acetonitrile/H₂O (1:1) solution. Since rhodium complexes 1 and 2 are used for the first time as catalysts in this type of systems, a systematic study was performed in order to elucidate the best conditions for H₂ production. Upon visible irradiation hydrogen production was detected and the best results were obtained at pH 7 when dye P3 and catalyst 1 were used with a TON of 61, after 48 h and in the presence of dye P1 and catalyst 2 with a TON of 69, after the 48 h.

A series of first-row transition metal complexes of tetrakis(pentafluorophenyl)porphyrin (1), denoted as 1-M (M$=$Mn, Fe, Co, Ni, Cu, and Zn), were synthesized and examined as electrocatalysts for the hydrogen evolution reaction (HER). All these transition metal porphyrins were shown to be active for HER in acetonitrile using trifluoroacetic acid (TFA) as the proton source. The molecular nature and the stability of these metal porphyrins when functioning as HER catalysts were confirmed, and all catalysts gave Faradaic efficiency of >97% for H₂ generation during bulk electrolysis. Importantly, by using 1-Cu, a remarkably high turnover frequency (TOF) of 48500 s${}^{-1}$1-Cu the most efficient among this series of metal porphyrin catalysts. This TOF value also represents one of the highest values reported in the literature. In addition, electrochemical analysis demonstrated that catalytic HER mechanisms with these 1-M complexes are different. These results show that with the same porphyrin ligand, the change of metal ions will have significant impact on both catalytic efficiency and mechanism. This work for the first time provides direct comparison of electrocatalytic HER features of transition metal complexes of tetrakis(pentafluorophenyl)porphyrin under identical conditions, and will be valuable for future design and development of more efficient HER electrocatalysts of this series.

In this study, four meso-expanded Co(III)corroles at meta-positions through Suzuki–Miyaura coupling reactions and their structural characterization are successfully accomplished and reported. An analysis of the structure–property relationships by spectroscopy, electrochemistry and electrochemical catalysis demonstrate how the positional isomerism influence the electronic structure and their catalytic behaviors of hydrogen evolution reactions (HERs) and oxygen reduction reactions (ORRs).

The electrochemical properties of $\beta$-octaethylporphycene iridium complex (Ir-OEPo) were determined. Based on the electro-spectro measurement results, the reduction of Ir-OEPo did not occur at the central metal but at the ligand, while the reduction of $\beta$-octaethylporphyrin iridium complex (Ir-OEPor) occurred at the central iridium. A catalytic current was observed during the cyclic voltammetry (CV) measurements with trifluoroacetic acid (TFA) under a reductive condition, indicating the catalytic reactivity of Ir-OEPo for the hydrogen evolution reaction (HER). By constant potential electrolysis, hydrogen gas was detected by gas chromatography (GC) and the catalytic reactivity of Ir-OEPo was confirmed. The HER mechanism via ligand reduction of macrocyclic aromatic complexes could be one of the concepts for the development of new catalysts.

CeO_x/C supported PtCu thin film catalysts were prepared by ion beam sputtering (IBS) and subsequently annealed at 400°C under vacuum environment and electrochemically dealloyed. Scanning transmission electronic microscope (STEM) and atomic force microscope (AFM) characterizations show that the surface of post-processed catalyst presents nanoporous structure and has a high root mean square roughness (RMS = 13.9nm). Electrochemical measurements indicate that the post-processed PtCu–CeO_x/C catalyst shows higher catalytic activity towards hydrogen evolution reaction than pure Pt/C. While inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis displays that the platinum (Pt) loading of the post-processed PtCu–CeO_x/C is 0.1192mg/cm², decreasing by 20% compare to pure Pt/C (0.1490mg/cm²). X-ray photoelectron spectroscopy (XPS) analysis confirms that the surface of post-processed PtCu–CeO_x/C enrich Pt and analyzes the chemical valence of Pt element using depth profiling technology. It can be inferred that the enhancement in catalytic property is attributed to the combined action between geometric structure effect and electronic modification effect of Pt atoms from CeO_x support.

LaFeO₃/NiO modified g-C₃N₄ nanosheets (L-N/CNS) were synthesized by a two-step method. HRTEM results showed that an intimate contact between LaFeO₃, NiO and N-CNS was successfully established. Ninety percent of phenol was degraded within 120min, and the hydrogen evolution rate of 171.2$\mu$molh${}^{-1}$g${}^{-1}$ was obtained over the L-N/CNS heterojunctions under the visible-light irradiation. It was higher than that of g-C₃N₄ nanosheets, NiO modified g-C₃N₄ and LaFeO₃/g-C₃N₄. The$\cdot$O${}_2^{-}$ radicals acted the crucial role in the photocatalytic degradation reaction. EIS, PL and time-resolved fluorescence spectra demonstrated that L-N/CNS possessed the highest charge separation efficiency. The intimate contact between LaFeO₃, NiO and g-C₃N₄ nanosheets promoted the separation and transfer of photo-induced electron–hole pairs and consequently prolonged the exciton lifetime, and implied more photo-induced electrons could be probably involved in the photocatalytic reactions on the surface of photocatalysts. Thus, the visible-light driven photocatalytic performances of L-N/CNS were effective. This work provided a feasible method to design and construct heterostructures for the exploitation of solar energy.

Preventing the high recombination rate of carriers in graphite-carbon nitride (GCN) is essential for hydrogen production. In this work, we break the original symmetry of GCN by embedding benzene ring for enhanced visible-light absorption and carriers transfer efficiency. The new catalyst was prepared by a condensation reaction using dicyandiamide and 5-amino-2,4,6-triiodoisophthalic acid as precursors. It shows photocatalytic hydrogen evolution rate of 690.74$\mu$molg${}^{-1}$h${}^{-1}$, 9.3 times enhancement than the original GCN. This work provides a new strategy for designing efficient two-dimensional photocatalytic materials for water splitting.

In this work, we investigated fabrication of porous nickel–silica composite particles through catalytic hydrogen evolution reaction from aqueous solution including sodium borohydride and ammonia borane. Aggregated nickel species were observed in the samples with high nickel content from scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) results, indicating that dispersion of active nickel species was significantly influenced by nickel content. The dispersion influenced hydrogen evolution amount and rate from aqueous solution including sodium borohydride and ammonia borane, and the samples with highly dispersed active nickel species showed high hydrogen evolution amount. The particles after the hydrogen evolution process showed significantly high specific surface area with large number of nanopores. UV-Vis spectra of the samples after the hydrogen evolution process indicated that the particles with high hydrogen evolution amount from aqueous solution including sodium borohydride and ammonia borane included high amount of reduced nickel species.

Carbonized melamine foam (CM) was used as an ideal framework for the in-situ growth of MoS₂ by hydrothermal method. And its hydrogen evolution reaction (HER) and the catalytic mechanism were explored. By regulating the concentration of the precursor, the stacking pattern of MoS₂ lamella on CM was optimized. And the results show that the sample with a precursor concentration of $2\times 10^{-2}$M possesses the smallest overpotential (218mV @ 10mAcm${}^{-2}$) and its vertical arrayed nanosheets encased on the surface of carbon matrix provide more sites for the absorption of H${}^{+}$ in the electrolyte which accounts for the promotion of hydrogen generation.

Efficient hydrogen production is a fundamental requirement of a future hydrogen economy. Utilization of highly active non-precious metal-based electrocatalysts has made electrolysis of water a promising candidate to generate hydrogen with low cost and high efficiency. Very recently, layered transition-metal disulfides (LTMDs) have been proven to be high-performance electrocatalysts with high activity and high stability for electrochemical hydrogen evolution. In this chapter, an overview of recent developments of LTMDs nanomaterials as catalysts for hydrogen evolution with high activity and stability is presented. The structural features and properties as well as their synthetic methods of LTMDs are briefly discussed. Then, we will highlight a variety of specific strategies to further improve the catalytic efficiency and stability of LTMDs by structure engineering, composition optimizing, and phase tailoring.

Transition-metal carbides (TMCs) have received widespread attention as noble-metal-free electrocatalysts for hydrogen evolution reactions (HER). However, the strong binding energy of adsorbed H on TMCs unfortunately prohibits the inherent activity. Thus, it’s necessary to regulate the electronic configurations of TMCs to improve HER activities. One of the effective strategies is doping TMCs with heteroatoms. In this chapter, we introduce the representative progress of doped TMCs for HER, with an emphasis on the functionalities toward electronic modulation and electrocatalysis promotion. The doping into TMCs by metal atoms and non-metal elements is discussed successively.