Positive direction of polarization-induced electric field improves formic acid electrooxidation on Pd

Adjusting the adsorption energy of adsorbates on catalyst can directly regulate the catalytic performance and reaction pathways of heterogeneous catalysis.Herein,we report a novel strategy,introducing polarization-induced electric field(PIEF)with different directions,to manipulate the adsorption energy of intermediates and reaction pathway of formic acid electrooxidation on Pd.Tourmaline nanoparticles are applied as the PIEF provider,of which the direction is successfully controlled via aligning the dipoles in tourmaline in a strong external electric field.Experimental and theoretical results systematically reveal that positive PIEF leads to an electron-deficient state of Pd,reduced adsorption energy of COad,enhanced adsorption energy of*HCOOH and*OH,and promoted formate pathway of formic acid electrooxidation.Pd/TNP+/FTO,with the aid of positive PIEF,shows three-fold enhancement in the formic acid electrooxidation(4.74 mA·cm^(−2))with high durability and anti-poisoning ability compared with pristine Pd.This study leads a new route to design formic acid electrocatalysts and provides an understanding on how to control the adsorption energy of adsorbates on electrocatalysts by an internal electric field.

Universal converse flexoelectricity in dielectric materials via varying electric field direction

Flexoelectricity is a symmetry independent electromechanical cou-pling phenomenon that outperforms piezoelectricity at micro and nanoscales due to its size-dependent behavior arising from gradi-ent terms in its constitutive relations.However,due to this gradient term flexoelectricity,to exhibit itself,requires specially designed geometry or material composition of the dielectric material.First of its kind,the present study put forward a novel strategy of achieving electric field gradient and thereby converse flexoelectri-city,independent of geometry and material composition of the material.The spatial variation of the electric field is established inside the dielectric material,Ba_(0.67)Sr_(0.33)TiO_(3)(BST),by manipulating electrical boundary conditions.Three unique patterns of electrode placement are suggested to achieve this spatial variation.This varying direction of electric field gives rise to electric field gradient,the prerequisite of converse flexoelectricity.A multi-physics cou-pling based theoretical framework is established to solve the flexo-electric actuation by employing isogeometric analysis(IGA).Electromechanically coupled equations of flexoelectricity are solved to obtain the electric field distribution and the resulting displace-ments thereby.The maximum displacements of 0.2 nm and 2.36 nm are obtained with patterns I and II,respectively,while pattern III can yield up to 85 nm of maximum displacement.

Effect of electroosmotic flow on brine imbibition in porous media

Based on Darcy＇s Law and the Helmholta-Smoluchowski equation, an imbibition velocity formula for the water phase with an electric field was deduced, showing that the imbibition velocity with an electric field is to various extents not only related to the rock permeability and characteristic length, the fluid viscosity, the oil-water interface tension and the gravity of the imbibing brine, but also to the fluid dielectric permittivity, zeta potential, applied electric field direction, and strength. Imbibition experiments with electric fields that are different in direction and strength were conducted, showing that application of a positive electric field enhances the imbibition velocity and increases the imbibition recovery ratio, while application of a negative electric field reduces the imbibition velocity and decreases the imbibition recovery ratio. The imbibition recovery ratio with a positive electric field increases with the strength of the electric field, and the imbibition recovery ratio with a negative electric field is lower than that without an electric field.

Construction of multi-homojunction TiO_(2)nanotubes for boosting photocatalytic hydrogen evolution by steering photogenerated charge transfer

As an effective means to improve charge carrier separation efficiency and directional transport,the gradient doping of foreign elements to build multi-homojunction structures inside catalysts has received wide attentions.Herein,we reported a simple and robust method to construct multi-homojunctions in black TiO_(2) nanotubes by the gradient doping of Ni species through the diffusion of deposited Ni element on the top of black TiO2 nanotubes driven by a high temperature annealing process.The gradient Ni distribution created parts of different Fermi energy levels and energy band structures within the same black TiO_(2) nanotube,which subsequently formed two series of multi-homojunctions within it.This special multi-homojunction structure largely enhanced the charge carrier separation and transportation,while the low concentration of defect states near the surface layer further inhibited carrier recombination and facilitated the surface reaction.Thus,the B-TNT-2Ni sample with the optimized Ni doping concentration exhibited an enhanced hydrogen evolution rate of~1.84 mmol·g^(−1)·h^(−1)under visible light irradiation without the assistance of noble-metal cocatalysts,~four times higher than that of the pristine black TiO_(2)nanotube array.With the capability to create multi-homojunction structures,this approach could be readily applied to various dopant systems and catalyst materials for a broad range of technical applications.