Solar Fuels: Visible-Light-Driven Generation of Dihydrogen at p-Type Silicon Electrocatalysed by Molybdenum Hydrides

We show that a robust molybdenum hydride system can sustain photoelectrocatalysis of a hydrogen evolution reaction at boron-doped, hydrogen-terminated, p-type silicon. The photovoltage for the system is about 600-650?mV and the current densities, which can be sustained at the photocathode in non-catalytic and catalytic regimes, are similar to those at a photoinert vitreous carbon electrode. The kinetics of electrocatalysed hydrogen evolution at the photocathode are also very similar to those measured at vitreous carbon-evidently visible light does not significantly perturb the catalytic mechanism. Importantly, we show that the doped (1-10?Ω?cm) p-type Si can function perfectly well in the dark as an ohmic conductor and this has allowed direct comparison of the cyclic voltammetric behaviour of the response of the system under dark and illuminated conditions at the same electrode. The p-type Si we have employed optimally harvests light energy in the 600-700?nm region and with 37?mW?cm(-2) illumination in this range; the light to electrochemical energy conversion is estimated to be 2.8?%. The current yield of hydrogen under broad tungsten halide lamp illumination at 90?mW?cm(-2) is (91±5)?% with a corresponding chemical yield of (98±5)?%.     

Solar Fuels: Photoelectrosynthesis of CO from CO2 at p‐Type Si using Fe Porphyrin Electrocatalysts

Photoelectrocatalytic conversion of CO₂ to CO can be driven at a boron‐doped, hydrogen terminated, p‐type silicon electrode using a meso‐tetraphenylporphyrin Fe^III chloride in the presence of CF₃CH₂OH as a proton source and 0.1 M [NBu₄][BF₄]/MeCN/5 % DMF (v/v) as the electrolyte. Under illumination with polychromatic light, the photoelectrocatalysis operates with a photovoltage of about 650 mV positive of that for the dark reaction. Carbon monoxide is produced with a current efficiency >90 % and with a high selectivity over H₂ formation. Photoelectrochemical current densities of 3 mA cm^?2 at ?1.1 V versus SCE are typical, and 175 turnovers have been attained over a 6 h period. Cyclic voltammetric data are consistent with a turnover frequency of ${k{{{\rm Si}\hfill \atop {\rm obs}\hfill}}}$ =0.24×10⁴ s^?1 for the photoelectrocatalysis at p‐type Si at ?1.2 V versus SCE this compares with ${k{{{\rm C}\hfill \atop {\rm obs}\hfill}}}$ =1.03×10⁴ s^?1 for the electrocatalysis in the dark on vitreous carbon at a potential of ?1.85 V versus SCE.     

From Solar Energy to Fuels: Recent Advances in Light‐Driven C1 Chemistry

Catalytic C₁ chemistry based on the activation/conversion of synthesis gas (CO+H₂), methane, carbon dioxide, and methanol offers great potential for the sustainable development of hydrocarbon fuels to replace oil, coal, and natural gas. Traditional thermal catalytic processes used for C₁ transformations require high temperatures and pressures, thereby carrying a significant carbon footprint. In comparison, solar‐driven C₁ catalysis offers a greener and more sustainable pathway for manufacturing fuels and other commodity chemicals, although conversion efficiencies are currently too low to justify industry investment. In this Review, we highlight recent advances and milestones in light‐driven C₁ chemistry, including solar Fischer–Tropsch synthesis, the water‐gas‐shift reaction, CO₂ hydrogenation, as well as methane and methanol conversion reactions. Particular emphasis is placed on the rational design of catalysts, structure–reactivity relationships, as well as reaction mechanisms. Strategies for scaling up solar‐driven C₁ processes are also discussed.     

Hydrogenation of Imines Catalyzed by Trisphosphine‐Substituted Molybdenum and Tungsten Nitrosyl Hydrides and Co‐Catalytic Acid

Hydride complexes Mo,W(CO)(NO)H(mer‐etpⁱp) (iPr₂PCH₂CH₂)₂PPh=etpⁱp) ( 2 a,b(syn) , syn and anti of NO and Ph(etpⁱp) orientions) were prepared and probed in imine hydrogenations together with co‐catalytic [H(Et₂O)₂][B(C₆F₅)₄] (140 °C, 60 bar H₂). 2 a,b(syn) were obtained via reduction of syn/anti‐Mo,W(NO)Cl₃(mer‐etpⁱp) and syn,anti‐Mo,W(NO)(CO)Cl(mer‐etpⁱp). [H(Et₂O)₂][B(C₆F₅)₄] in THF converted the hydrides into THF complexes syn‐[Mo,W(NO)(CO)(etpⁱp)(THF)][B(C₆F₅)₄]. Combinations of the p‐substituents of aryl imines p‐R¹C₆H₄CH=N‐p‐C₆H₄R² (R¹,R²=H,F,Cl,OMe,α‐Np) were hydrogenated to amines (maximum initial TOFs of 1960 h^?1 ( 2 a(syn) ) and 740 h^?1 ( 2 b(syn) ) for N‐(4‐methoxybenzylidene)aniline). An ‘ionic hydrogenation’ mechanism based on linear Hammett plots (ρ=?10.5, p‐substitution on the C‐side and ρ=0.86, p‐substitution on the N‐side), iminium intermediates, linear P(H₂) dependence, and DKIE=1.38 is proposed. Heterolytic splitting of H₂ followed by ‘proton before hydride’ transfers are the steps in the ionic mechanism where H₂ ligand addition is rate limiting.     

Room‐Temperature and Aqueous‐Phase Synthesis of Plasmonic Molybdenum Oxide Nanoparticles for Visible‐Light‐Enhanced Hydrogen Generation

A straightforward aqueous synthesis of MoO_3?x nanoparticles at room temperature was developed by using (NH₄)₆Mo₇O₂₄?4 H₂O and MoCl₅ as precursors in the absence of reductants, inert gas, and organic solvents. SEM and TEM images indicate the as‐prepared products are nanoparticles with diameters of 90–180 nm. The diffuse reflectance UV‐visible‐near‐IR spectra of the samples indicate localized surface plasmon resonance (LSPR) properties generated by the introduction of oxygen vacancies. Owing to its strong plasmonic absorption in the visible‐light and near‐infrared region, such nanostructures exhibit an enhancement of activity toward visible‐light catalytic hydrogen generation. MoO_3?x nanoparticles synthesized with a molar ratio of Mo^VI/Mo^V 1:1 show the highest yield of H₂ evolution. The cycling catalytic performance has been investigated to indicate the structural and chemical stability of the as‐prepared plasmonic MoO_3?x nanoparticles, which reveals its potential application in visible‐light catalytic hydrogen production.     

钼蓝分光光度法测定铅精矿中二氧化硅

采用钼蓝分光光度法测定铅精矿中二氧化硅的含量,研究了显色酸度、钼酸铵用量、加入钼酸铵后的稳定时间、还原液用量以及加入还原液后稳定时间等因素对测定的影响,确定了最佳测定条件。方法加标回收率在97.01%~103.8%,相对标准偏差(RSD)在1.3%~8.5%。方法操作简单,流程短,干扰少,具有较好的精密度和准确度,能够满足铅精矿中二氧化硅含量的测定。     

Solar Electricity and Solar Fuels: Status and Perspectives in the Context of the Energy Transition

The energy transition from fossil fuels to renewables is already ongoing, but it will be a long and difficult process because the energy system is a gigantic and complex machine. Key renewable energy production data show the remarkable growth of solar electricity technologies and indicate that crystalline silicon photovoltaics (PV) and wind turbines are the workhorses of the first wave of renewable energy deployment on the TW scale around the globe. The other PV alternatives (e.g., copper/indium/gallium/selenide (CIGS) or CdTe), along with other less mature options, are critically analyzed. As far as fuels are concerned, the situation is significantly more complex because making chemicals with sunshine is far more complicated than generating electric current. The prime solar artificial fuel is molecular hydrogen, which is characterized by an excellent combination of chemical and physical properties. The routes to make it from solar energy (photoelectrochemical cells (PEC), dye‐sensitized photoelectrochemical cells (DSPEC), PV electrolyzers) and then synthetic liquid fuels are presented, with discussion on economic aspects. The interconversion between electricity and hydrogen, two energy carriers directly produced by sunlight, will be a key tool to distribute renewable energies with the highest flexibility. The discussion takes into account two concepts that are often overlooked: the energy return on investment (EROI) and the limited availability of natural resources—particularly minerals—which are needed to manufacture energy converters and storage devices on a multi‐TW scale.     

Constant Electricity Generation in Nanostructured Silicon by Evaporation‐Driven Water Flow

Recently, hydrovoltaic technology emerged as a novel renewable energy harvesting method, which dramatically extends the capability to harvest water energy. However, the urgent issue restricting its device performance is poor carrier transport properties of the solid surface if large charged interface is considered simultaneously. Herein, a hydrovoltaic device based on silicon nanowire arrays (SiNWs), which provide large charged surface/volume ratio and excellent carrier transport properties, yields sustained electricity by a carrier concentration gradient induced by evaporation‐induced water flow inside nanochannels. The device can yield direct current with a short‐circuit current density of over 55 μA cm^?2, which is three orders larger than a previously reported analogous device (approximately 40 nA cm^?2). Moreover, it exhibits a constant output power density of over 6 μW cm^?2 and an open‐circuit voltage of up to 400 mV. Our finding may pave a way for developing energy‐harvesting devices from ubiquitous evaporation‐driven internal water flow in nature with semiconductor material of silicon.     

Visible‐Light‐Driven Water Oxidation by a Molecular Manganese Vanadium Oxide Cluster

Photosynthetic water oxidation in plants occurs at an inorganic calcium manganese oxo cluster, which is known as the oxygen evolving complex (OEC), in photosystem II. Herein, we report a synthetic OEC model based on a molecular manganese vanadium oxide cluster, [Mn₄V₄O₁₇(OAc)₃]^3?. The compound is based on a [Mn₄O₄]⁶⁺ cubane core, which catalyzes the homogeneous, visible‐light‐driven oxidation of water to molecular oxygen and is stabilized by a tripodal [V₄O₁₃]^6? polyoxovanadate and three acetate ligands. When combined with the photosensitizer [Ru(bpy)₃]²⁺ and the oxidant persulfate, visible‐light‐driven water oxidation with turnover numbers of approximately 1150 and turnover frequencies of about 1.75 s^?1 is observed. Electrochemical, mass‐spectrometric, and spectroscopic studies provide insight into the cluster stability and reactivity. This compound could serve as a model for the molecular structure and reactivity of the OEC and for heterogeneous metal oxide water‐oxidation catalysts.     

硅钼蓝光度法测定碳化硅中二氧化硅的含量

采用氯化钠-盐酸-氢氟酸溶解碳化硅样品,加钼酸铵使硅酸离子形成硅钼杂多酸,然后用1-氨基-2-萘酚-4-磺酸还原剂将其还原成硅钼蓝,在700nm波长处测定其吸光度,从而测得碳化硅中的二氧化硅含量。考察了称样量、水浴温度、水浴加热时间、样品储存容器、显色反应时间等因素对测定结果的影响,优化了测试条件。二氧化硅的质量浓度在0．25-12．5mg／（100mL）的范围内与吸光度呈良好的线性关系,线性相关系数r=0．99986。加标回收率为99．2％～100．9％,测定结果的相对标准偏差为0．76％（n=6）。     

Gold‐Nanoparticle‐Loaded Carbonate‐Modified Titanium(IV) Oxide Surface: Visible‐Light‐Driven Formation of Hydrogen Peroxide from Oxygen

Gold nanoparticle‐loaded rutile TiO₂ with a bimodal size distribution around 10.6 nm and 2.3 nm (BM‐Au/TiO₂) was prepared by the deposition precipitation and chemical reduction (DP‐CR) technique. Visible‐light irradiation (λ>430 nm) of the BM‐Au/TiO₂ plasmonic photocatalyst yields 35 μm H₂O₂ in aerated pure water at irradiation time (t_p)=1 h, and the H₂O₂ concentration increases to 640±60 μm by the addition of 4 % HCOOH as a sacrificing electron donor. Further, a carbonate‐modified surface BM‐Au/TiO₂ (BM‐Au/TiO₂‐CO₃^2?) generates a millimolar level of H₂O₂ at t_p=1 h with a quantum efficiency (Φ) of 5.4 % at λ=530 nm under the same conditions. The recycle experiments confirmed the stable performance of BM‐Au/TiO₂.     

A Crystalline Copper(II) Coordination Polymer for the Efficient Visible‐Light‐Driven Generation of Hydrogen

A crystalline coordination polymer (CP) photocatalyst (Cu‐RSH) which combines redox‐active copper centers with photoactive rhodamine‐derived ligands remains stable in acid and basic solutions from pH 2 to 14, and efficiently catalyzes dihydrogen evolution at a maximum rate of 7.88 mmol g^?1 h^?1 in the absence of a mediator and a co‐catalyst. Cyclic voltammetry, control experiments, and DFT calculations established that copper nodes with open coordination sites and favorable redox potentials, aided by spatially ordered stacking of rhodamine‐based linkers, account for the high catalytic performance of Cu‐RSH. Emission quenching, time‐resolved fluorescence decay, and transient photocurrent experiments disclosed the charge separation and transfer process in the catalytic system. The present study demonstrates the potential of crystalline copper CPs for the practical utilization of light.     

Visible‐Light‐Driven Aza‐ortho‐quinone Methide Generation for the Synthesis of Indoles in a Multicomponent Reaction

A visible‐light‐driven radical‐mediated strategy for the in situ generation of aza‐ortho ‐quinone methides from 2‐vinyl‐substituted anilines and alkyl radical precursors is described. This process enables an efficient multicomponent reaction of 2‐vinylanilines, halides, and sulfur ylides, and has a wide substrate scope and good functional group tolerance. Treatment of the cycloaddition products with a base leads to densely functionalized indoles in a single‐flask operation.     

Visible‐Light‐Driven,Tunable, Photoelectrochemical Performance of a Series of Metal‐Chelate,Dye‐Organized,Crystalline, CdS Nanoclusters

CdS nanoclusters of four different sizes were integrated with ruthenium‐complex dyes. The cluster–dye crystalline composites, [Cd₄(SPh)₁₀][Ru(bpy)₃], [Cd₈S(SPh)₁₆][Ru(bpy)₃], [Cd₈S(SPh)₁₃?Cl?(CH₃OCS₂)₂][Ru(phen)₃], [Cd₁₇S₄(SPh)₂₈][Ru(bpy)₃], and [Cd₃₂S₁₄(SPh)₄₀][Ru(phen)₃]₂ (phen=1,10‐phenanthroline and bpy=bipyridine), show intense absorption in the visible‐light region. They also exhibit size‐dependent photocurrent responses under the illumination of visible light. The photocurrent increases with increased cluster size. The dyes also have significant influence on the photocurrent generation of the composite.