Design of experiments unravels insights into selective ethylene or methane production on evaporated Cu catalysts

As a highly tempting technology to close the carbon cycle,electrochemical CO_(2)reduction calls for the development of highly efficient and durable electrocatalysts.In the current study,Design of Experiments utilizing the response surface method is exploited to predict the optimal process variables for preparing high-performance Cu catalysts,unraveling that the selectivity towards methane or ethylene can be simply modulated by varying the evaporation parameters,among which the Cu film thickness is the most pivotal factor to determine the product selectivity.The predicted optimal catalyst with a low Cu thickness affords a high methane Faradaic efficiency of 70.6%at the partial current density of 211.8 m A cm^(-2),whereas that of a high Cu thickness achieves a high ethylene selectivity of 66.8%at267.2 m A cm^(-2)in the flow cell.Further structure-performance correlation and in-situ electrospectroscopic measurements attribute the high methane selectivity to isolated Cu clusters with low packing density and monotonous lattice structure,and the high ethylene efficiency to coalesced Cu nanoparticles with rich grain boundaries and lattice defects.The high Cu packing density and crystallographic diversity is of essence to promoting C–C coupling by stabilizing*CO and suppressing*H coverage on the catalyst surface.This work highlights the implementation of scientific and mathematic methods to uncover optimal catalysts and mechanistic understandings toward selective electrochemical CO_(2)reduction.

Polypyrrole reinforced ZIF-67 with modulated facet exposure and billion-fold electrical conductivity enhancement towards robust photocatalytic CO_(2) reduction

The implementation of metal organic frameworks(MOFs) as the co-catalysts in hybrid photocatalytic systems puts requirements on both their charge-carrying capability and solvent stability. In the current study, in order to simultaneously promote the electrical conductivity and water stability of ZIF-67, an insitu monomer trapping strategy is deployed to synthesize polypyrrole(PPy)-reinforced ZIF-67 ensembles.Through coordination modulation, the incremental addition of pyrrole monomers enables to alter the crystal morphology of ZIF-67 from rhombic dodecahedra to truncated rhombic dodecahedra, and further to cubes. Upon polymerization, the resulted composite, in comparison to ZIF-67, demonstrates a billionfold conductivity enhancement, much improved chemical stability in pronated solvents, as well as largely retained specific surface area and porosity, enabling it functioning as an outstanding co-catalyst for catalyzing robust photocatalytic CO_(2) reduction. Furthermore, a PPy-mediated electron harvest and relay mechanism is proposed for rationalizing the enhanced photocatalytic performance.

Atomically dispersed Co-Cu alloy reconstructed from metalorganic framework to promote electrochemical CO_(2)methanation

Electroreduction of carbon dioxide into value-added fuels or chemicals using renewable energy helps to effectively reduce carbon dioxide emission and alleviate the greenhouse effect while storing intermittent energies.Due to the existing infrastructure of global natural gas utilization and distribution,methane produced in such a green route attracts wide interests.However,limited success has been witnessed in the practical application of catalysts imparting satisfactory methane activity and selectivity.Herein,we report the fabrication of an atomically dispersed Co-Cu alloy through the reconstruction of trace-Co doped Cu metalorganic framework.This catalyst exhibits a methane Faradaic efficiency of 60%±1%with the corresponding partial current density of 303±5 mA·cm^(−2).Operando X-ray adsorption spectroscopy and attenuated-total-reflection surface enhanced infrared spectroscopy unravel that the introduction of atomically dispersed Co in Cu favors*CO protonation via enhancing surface water activation,and suppresses C−C coupling by reducing*CO coverage,thereby leading to high methane selectivity.

Robust photocatalytic hydrogen production on metal-organic layers of Al-TCPP with ultrahigh turnover numbers

The development of robust photocatalytic systems is key to harvest the solar power for hydrogen production. In the current study, a series of aluminum-based porphyrinic metal organic frameworks (AlTCPP) with various morphologies of bulk, carambola-like and nanosheets are synthesized with modulated layer thickness. Morphology-dependent photocatalytic activities in hydrogen production are witnessed and inversely correlate to the thickness of the Al-TCPP micro-platelets or nanosheets. Particularly, the exfoliated metal organic layers (MOLs) of Al-TCPP demonstrated a high hydrogen yield rate of 1.32×10^(4)μmol h^(-1)g^(-1)that is 21-fold of that from the bulk catalyst, as well as an exceptional TON of6704 that seldom seen in literature. Through comprehensive photochemical characterizations, the remarkable photocatalytic performance of Al-TCPP-MOL is attributed to the great charge separation efficiency and transfer kinetics endowed by the ultrathin 2D morphology with extended active surface area.