CO2 electroreduction favors carbon isotope 12C over 13C and facilitates isotope separation.

We discovered that CO2 electroreduction strongly favors the conversion of the dominant isotope of carbon (12C) and discriminates against the less abundant, stable carbon 13C isotope. Both absorption of CO2 in the alkaline electrolyte and CO2 electrochemical reduction favor the lighter isotopologue. As a result, the stream of unreacted CO2 leaving the electrolyzer has an increased 13C content, and the depletion of 13C in the product is several times greater than that of photosynthesis. Using a natural abundance feed, we demonstrate enriching of the 13C fraction to ∼1.3% (i.e., +18%) in a single-pass reactor and propose a scalable and economically attractive process to yield isotopes of a commercial purity. Our finding opens pathways to both cheaper and less energy-intensive production of stable isotopes (13C, 15N) essential to the healthcare and chemistry research, and to an economically viable, disruptive application of electrolysis technologies developed in the context of sustainability transition.

Implanting Ni-O-VOx sites into Cu-doped Ni for low-overpotential alkaline hydrogen evolution.

Nickel-based catalysts are most commonly used in industrial alkaline water electrolysis. However, it remains a great challenge to address the sluggish reaction kinetics and severe deactivation problems of hydrogen evolution reaction (HER). Here, we show a Cu-doped Ni catalyst implanted with Ni-O-VOx sites (Ni(Cu)VOx) for alkaline HER. The optimal Ni(Cu)VOx electrode exhibits a near-zero onset overpotential and low overpotential of 21 mV to deliver -10 mA cm-2, which is comparable to benchmark Pt/C catalyst. Evidence for the formation of Ni-O-VOx sites in Ni(Cu)VOx is established by systematic X-ray absorption spectroscopy studies. The VOx can cause a substantial dampening of Ni lattice and create an enlarged electrochemically active surface area. First-principles calculations support that the Ni-O-VOx sites are superactive and can promote the charge redistribution from Ni to VOx, which greatly weakens the H-adsorption and H2 release free energy over Ni. This endows the Ni(Cu)VOx electrode high HER activity and long-term durability.

Manipulation of Charge Transport by Metallic V13 O16 Decorated on Bismuth Vanadate Photoelectrochemical Catalyst.

Conductive metal oxides represent a new category of functional material with vital importance for many modern applications. The present work introduces a new conductive metal oxide V13 O16 , which is synthesized via a simplified photoelectrochemical procedure and decorated onto the semiconducting photocatalyst BiVO4 in controlled mass percentages ranging from 25% to 37%. Owing to its excellent conductivity and good compatibility with oxide materials, the metallic V13 O16 -decorated BiVO4 hybrid catalyst shows a high photocurrent density of 2.2 ± 0.2 mA cm-2 at 1.23 V versus reversible hydrogen electrode (RHE). Both experimental characterization and density functional theory calculations indicate that the superior photocurrent derives from enhanced charge separation and transfer, resulting from ohmic contact at the interface of mixed phases and superior electrical conductivity from V13 O16 . A Co-Pi coating on BiVO4 -V13 O16 further increases the photocurrent to 5.0 ± 0.5 mA cm-2 at 1.23 V versus RHE, which is among the highest reported for BiVO4 -based photoelectrodes. Surface photovoltage and transient photocurrent measurements suggest a charge-transfer model in which photocurrents are enhanced by improved surface passivation, although the barrier at the Co-Pi/electrolyte interface limits the charge transfer.

Processable Surface Modification of Nickel-Heteroatom (N, S) Bridge Sites for Promoted Alkaline Hydrogen Evolution.

Nickel-heteroatoms bridge sites are important reaction descriptors for many catalytic and electrochemical processes. Herein we report the controllable surface modification of nickel-nitrogen (Ni-N) bridge sites on metallic Ni particles via a simplified vapor-assisted treatment approach. X-ray absorption spectroscopy (XAS) and Operando Raman spectroscopy verifies the interaction between Ni and surface-anchored N, which leads to distorted Ni lattice structure with improved wettability. The Ni-N bridge sites with appropriate N coverage level plays a critical role in the enhanced hydrogen evolution reaction (HER) and the optimized electrode (Ni-N0.19 ) has demonstrated superior HER performances with low overpotential merely of 42 mV for achieving a current density of 10 mA cm-2 , as well as favorable reaction kinetics and excellent durability in alkaline electrolyte. DFT calculations revealed that the appropriate N-coverage level can lead to the most favorable ΔGH* kinetics for both adsorption of H* and release of H2 , while high N coverage (Ni-N0.59 ) results in weaker H* adsorption, thus a decreased HER activity, corresponding well to our experimental observations. Furthermore, this generic synthetic approach can also be applied to prepare S-modified Ni HER catalyst by generating hydrogen sulfide vapor.

Photocatalytic materials and technologies for air purification.

Since there is increasing concern for the impact of air quality on human health, the present work surveys the materials and technologies for air purification using photocatalytic materials. The coverage includes (1) current photocatalytic materials for the decomposition of chemical contaminants and disinfection of pathogens present in air and (2) photocatalytic air purification systems that are used currently and under development. The present work focuses on five main themes. First, the mechanisms of photodegradation and photodisinfection are explained. Second, system designs for photocatalytic air purification are surveyed. Third, the photocatalytic materials used for air purification and their characteristics are considered, including both conventional and more recently developed photocatalysts. Fourth, the methods used to fabricate these materials are discussed. Fifth, the most significant coverage is devoted to materials design strategies aimed at improving the performance of photocatalysts for air purification. The review concludes with a brief consideration of promising future directions for materials research in photocatalysis.

Multivalence Charge Transfer in Doped and Codoped Photocatalytic TiO2.

The present work reports data for the mineralogical and chemical properties of anatase thin films individually doped or codoped with chromium and vanadium, fabricated by sol-gel spin coating on glass substrates and annealing at 450 °C for 2 h. X-ray photoelectron spectroscopy data indicated the presence of Ti(4+), Ti(3+), Cr(3+), and possibly Cr(4+) in the Cr-doped thin films; Ti(4+), Ti(3+), V(3+), V(4+), and possibly V(5+) in the V-doped thin films; and Ti(4+), Ti(3+), Cr(3+), Cr(4+), V(3+), V(4+), and possibly V(5+) in the codoped thin films. While the thermodynamically stable valences Ti(4+), Cr(3+), and V(5+) would be expected to have formed, the presence of the nonequilibrium valences Ti(3+), Cr(4+), V(3+), and V(4+) is considered to have resulted from intervalence charge transfer for the Cr-doped and V-doped systems but from multivalence charge transfer (MVCT) for the codoped system. The latter phenomenon, which is introduced as a new conceptual term, describes the nature of the mutual exchange of electrons during valence changes of both dopant (Cr, V) and matrix (Ti) ions during annealing. In the present case, MVCT appears to be a transient metastable condition that acts during annealing, but subsequent UV irradiation can alter its effects.