No abstract

Recent applications of photoelectrochemistry at the semiconductor/ liquid interface provide a renewable route of mimicking natural photosynthesis and yielding chemicals from sunlight, water, and air. Nanowires, defined as one-dimensional nanostructures, exhibit multiple unique features for photoelectrochemical applications and promise better performance as compared to their bulk counterparts. This article reviews the use of semiconductor nanowires in photoelectrochemistry. After introducing fundamental concepts essential to understanding nanowires and photoelectrochemistry, the review considers answers to the following questions: (1) How can we interface semiconductor nanowires with other building blocks for enhanced photoelectrochemical responses? (2) How are nanowires utilized for photoelectrochemical half reactions? (3) What are the techniques that allow us to obtain fundamental insights of photoelectrochemistry at single-nanowire level? (4) What are the design strategies for an integrated nanosystem that mimics a closed cycle in artificial photosynthesis? This framework should help readers evaluate the salient features of nanowires for photoelectrochemical applications, promoting the sustainable development of solar-powered chemical plants that will benefit our society in the long run.

The abundant yet widely distributed methane resources require efficient conversion of methane into liquid chemicals, whereas an ambient selective process with minimal infrastructure support remains to be demonstrated. Here we report selective electrochemical oxidation of CH 4 to methyl bisulfate (CH 3 OSO 3 H) at ambient pressure and room temperature with a molecular catalyst of vanadium (V)-oxo dimer. This water-tolerant, earthabundant catalyst possesses a low activation energy (10.8 kcal mol-1) and a high turnover frequency (483 and 1336 hr −1 at 1-bar and 3-bar pure CH 4 , respectively). The catalytic system electrochemically converts natural gas mixture into liquid products under ambient conditions over 240 h with a Faradaic efficiency of 90% and turnover numbers exceeding 100,000. This tentatively proposed mechanism is applicable to other d 0 early transition metal species and represents a new scalable approach that helps mitigate the flaring or direct emission of natural gas at remote locations.

Although most class (b) transition metals have been studied in regardt oC H 4 activation, divalent silver (Ag II ), possibly owing to its reactive nature,isthe only class (b) highvalent transition metal center that is not yet reported to exhibit reactivities towards CH 4 activation. We now report that electrochemically generated Ag II metalloradical readily functionalizes CH 4 into methyl bisulfate (CH 3 OSO 3 H) at ambient conditions in 98 %H 2 SO 4 .M echanistic investigation experimentally unveils al ow activation energy of 13.1 kcal mol À1 , ahigh pseudo-first-order rate constant of CH 4 activation up to 2.8 10 3 h À1 at room temperature and aCH 4 pressure of 85 psi, and two competing reaction pathwayspreferable towards CH 4 activation over solvent oxidation. Reaction kinetic data suggest aF aradaic efficiency exceeding 99 %b eyond 180 psi CH 4 at room temperature for potential chemical production from widely distributed natural gas resources with minimal infrastructure reliance.electrophilicity may be reactive towards CH 4 via either electrophilic activation [6] or ar adical-based mechanism. [7] Consistently,many high-valent class (b) metals in the d-block of periodic table,i ncluding Rh I,II , [8] Pd II,III , [9] Ir III , [10] Pt II,IV , [11] Au I,III , [12] Hg II , [6b] have been reported for CH 4 activation (Figure 1a). Some of the borderline metals with intermediate chemical softness,i ncluding Mn III , [13] Co III , [13] Ru IV,VIII , [14] Os IV,VIII , [15] Tl III , [6c] and Pb IV , [6c, 13] are reactive towards CH 4 , too.Yet there is one exception, silver (Ag). While monovalent Ag I as am ild oxidant (h = 6.96; E8 8 = 0.80 Vv s. normal hydrogen electrode (NHE) for Ag + (aq.)/Ag (s)) [5,16] may not be oxidative enough to break the CÀHb ond in CH 4 (E8 8 = 0.59 Vvs. NHE for CH 3 OH (l)/CH 4 (g)), [2b, 16] divalent Ag II is similarly soft (h = 6.7) [5] and possesses aA g II /Ag I redox potential (E8 8 % 2.5 Vv s. NHE for Ag II /Ag I in 98 % H 2 SO 4 ) [17] comparable to other reported CH 4 -activation catalysts. [2a,b,9b] Therefore,i ti si ntriguing that divalent Ag II has not been known for CH 4 activation despite the reported Ag II -based reactivities on much weaker C À Hbonds in organic synthesis. [18] Thed 9 electronic configuration of Ag II not only renders it am etalloradical, but also introduces the Jahn-Te ller effect in an O h ligand field that elongates the ligand bond in the axial position (Figure 1b). [19] Such weakly bound axial ligands and Ag II sl ikely radical nature may offer an opportunity for substrate binding and CH 4 activation in aradical-based activation pathway with low reaction barrier, leading to our hypothesis that Ag II ,o nce continuously generated, may serve as the active species towards ambient CH 4 functionalization catalytically.Our strategy of investigating Ag II as ap otential active species towards CH 4 activation includes continuous electrogeneration of reactive Ag II species in an inert solvent environment (Figure 1c). Electrochemistry offers av iable and clean ...

The development of catalysts for electrochemical dinitrogen reduction has so far focused on metal-based compounds and materials. In a recent report published in Joule, Zheng and colleagues demonstrated that boron-doped graphene electrochemically reduces dinitrogen in aqueous solution under ambient conditions.