3.7 Photosystem II from T. vulcanus (PDB ID: 3WU2, a) and major redox‐active components within a PS‐II monomer involved in the main‐pathway electron transfer indicated with red arrows (b).Figure 3.8 The cycle of intermediate oxidation states of the oxygen‐evolving complex. Water is assumed to bind at the S3 state of the cluster and upon reconstitution of the S0 state. The S4 state is a postulated but unobserved transient intermediate that decays spontaneously to S0 with release of dioxygen.Figure 3.9 The Mn4CaO5 cluster and its protein pocket in the dark‐stable S1 state as revealed by protein crystallography (PDB ID: 3WU2, a), and a scheme showing the commonly used labeling of the ions comprising the inorganic core.Figure 3.10 Proposed models for the inorganic core in the S2 state of the OEC, with the first coordination sphere mostly omitted for clarity. The different magnetic topologies of the two valence isomers, as expressed through the pairwise exchange coupling constants Jij (values shown in cm−1; J < 0 is antiferromagnetic coupling), lead to different total spin states and g values for the corresponding EPR signals.Figure 3.11 The S2 → S3 transition according to Retegan et al. [191] and possible isovalent Mn(IV)4 components of the S3 state; the superscript “W” indicates binding of an additional water ligand.Figure 3.12 Two selected scenarios for the nature of the S4 state and OO bond formation from the computational literature: (a) formation of a Mn1(IV)‐oxyl group in the S4 state is followed by odd‐electron radical oxyl–oxo coupling [285], and (b) formation of a five‐coordinate high‐spin Mn4(V)‐oxo is followed by intramolecular nucleophilic coupling with concerted water binding [289]. Thick lines indicate direction of Jahn–Teller axes of Mn(III) ions.Figure 3.13 Reaction mechanism of RuBisCO proposed by Taylor and Andersson. Source: Taylor and Andersson [351].
3 Chapter 4Figure 4.1 Schematic illustration of photocatalytic hydrogen generation over a semiconductor photocatalyst [8].Figure 4.2 Band levels of various semiconductor photocatalysts. Source: Lu et al. [15].Figure 4.3 Schematic cells for rutile phase (a) and anatase phase (b) of TiO2. Source: Thompson and Yates [16].Figure 4.4 Photocatalytic H2 evolution of pure TiO2, Degussa P25, and TiO2 with different amounts of Zn. Source: Al‐Mayman et al. [25].Figure 4.5 Hydrogen evolution on the bare and metallic TiO2 photocatalysts using the benchmark Degussa P25 TiO2 and its bimetallic materials as the references. Source: Wang et al. [26].Figure 4.6 Photocatalytic hydrogen evolution on TiO2‐supported Au–Pd nanoparticles using a range of alcohols. Source: Su et al. [27].Figure 4.7 Schematic representation of the band structure of pure and N‐doped anatase TiO2. Note that the energies are not in scale. Source: Di Valentin et al. [32].Figure 4.8 The photocatalyst H2 generation rate of 2.5 wt%‐Cu2O/TiO2 with different sacrificial reagents. Source: Li et al. [34].Figure 4.9 (a) The energy band structure of ZnO/ZnS heterojunction. (b) The graphic structure of ZnO‐dotted ZnS. Source: Wu et al. [37].Figure 4.10 Tri‐s‐triazine‐based structure of g‐C3N4. The C and N atoms are indicated by gray and blue balls [8].Figure 4.11 Photocatalytic H2 production over the bulk C3N4, C3N4 NSs, and C3N4 NTs under visible‐light irradiation. Source: Zhu et al. [54].Figure 4.12 Graphic design of preparation of cobalt‐doped g‐C3N4. Source: Chen et al. [57].Figure 4.13 (a) EIS, (b) photocurrent response, and steady‐state (c) and transient (d) PL spectra of g‐C3N4 and B‐doped g‐C3N4 samples. Source: Chen et al. [60].Figure 4.14 Schematic illustration of the charge transfer for the three types of heterojunctions [8].Figure 4.15 Graphic illustration of the proposed mechanism for cobalt oxide/C3N4 NT heterojunction for photocatalytic H2 evolution. Source: Zhu et al. [61].Figure 4.16 Schematic diagram of the photocatalytic mechanism in WO3/MCN. Source: Kailasam et al. [63].Figure 4.17 The average H2 evolution rate of the SiC nanowires and modified SiC nanowires. Source: Hao et al. [66].Figure 4.18 Illustration of lanthanide upconversion nanoparticles (UCNPs).Figure 4.19 Illustrative diagrams of energy transfer among NYFG(15)/C3N4 NTs. Source: Zhu et al. [67].Figure 4.20 The proposed mechanism of the improved photocatalytic activity in the N‐CDs/CdS photocatalyst. Source: Shi et al. [69].Figure 4.21 Graphic diagram of the FeS2–TiO2 heterostructures under ultraviolet, visible, and NIR light irradiation for photocatalytic H2 evolution. Source: Kuo et al. [71].Figure 4.22 (a) The UV–vis near‐infrared absorption spectrum. (b) Photocatalytic hydrogen evolution for amorphous TiO2–x. Source: Jiang et al. [74]Figure 4.23 Methanol and its dissociative species underwent two‐electron oxidation in photocatalytic H2 production process over Au–Pt alloyed TiO2 nanocomposites. Source: Al‐Mayman et al. [25].
4 Chapter 5Figure 5.1 The schematic illustration of the features of H2 production by PV + EC, PEC, and PC in the five aspects of cost, STH efficiency, technology readiness, H2/O2 separation, and catalyst stability.Figure 5.2 The schematic illustration of three steps in PEC water splitting process. Source: From Wang and Wang [7]. © 2018 Elsevier.Figure 5.3 The illustration of semiconductor–electrolyte interface and the corresponding band bending. (a, b) The scheme and energy level of semiconductor and electrolyte in vacuum. The electrons are uniformly distributed around the core of atoms (blue dot). (c, d) The schematic illustration of electron distribution and the energy band bending when SEI is built. The electrons (red dot) are accumulated at the SEI interface. (e, f) The schematic illustration of electron–hole separation and transfer under illumination.Figure 5.4 (a) The oxygen vacancy concentration change by adjusting the treatment duration in N2. (b) The volcano relationship between photocurrent and oxygen vacancy concentration. Source: Wang et al. [39]. © 2019 Willey.Figure 5.5 (a) The schematic charge transfer in particulate Ta3N5 photoanode. (b) The change of charge separation and transfer efficiency for Ta3N5 photoanode when the charge transfer and generation are improved gradually. Source: Wang et al. [45]. Licensed under CC BY 3.0 Unported.Figure 5.6 (a) The image and (b) the photoresponse (red curve) of branched 2D porous TiO2 single‐crystal nanosheet photoelectrode. Insert (a) illustrates the photocharge transfer during PEC process. Source: Butburee et al. [71]. Reproduced with the permission from Wiley.Figure 5.7 (a) The surface state distribution characterization by cyclic voltammetry (CV) and the surface state related capacitance (Css). The different hematite photoelectrodes are compared including Ti doping, Al2O3 passivation, and H2O2 treatment. (b) The schematic illustration of PEC reaction via the surface states as intermediates. Source: From Wang et al. [8]. © 2016 Royal Society of Chemistry.Figure 5.8 The schematic illustration of cocatalyst design strategy based on a charge storage layer between the semiconductor and the effective cocatalyst layer.Figure 5.9 The schematic illustration of three different types of unbiased PEC water splitting systems. PA, PC, and PV represent photoanode, photocathode, and photovoltaic, respectively. The j–E curves represent their photoresponses in a three‐electrode system. The intersections (red dots) indicate the unbiased operation points.
5 Chapter 6Figure 6.1 Schematic illustration of photocatalytic oxygen evolution systems: (a) homogeneous and (b) heterogeneous configuration.Figure 6.2 Structures of (a) PS‐II‐OEC natural WOCs and (b) λ‐MnO2, (c) Mn4O4L6 core, and (d) Co4O4(Ac)4(py)4 artificial WOCs. Source: From McCool et al. [27]. © 2011 American Chemical Society.Figure 6.3 Ball‐and‐stick model of (a) Mn4POM core, (b) polyhedral Mn4POM, and (c) S0 state of the natural OEC model. (d) Cycle diagram for the electron transfer within the S0 → S4 Kok cycle of the natural PS‐II‐OEC. (e) Photocatalytic oxygen evolution of Mn4POM within the [Ru(bpy)3]2+/Na2S2O8