Electrolyte Effect on Photoetching of Gallium Nitride

The limited material removal rate of conventional chemical mechanical polishing(CMP)significantly hinders the fabrica-tion efficiency and surface quality,thereby preventing the development of gallium nitride(GaN)-based devices.Moreover,the incorporation of photoelectrochemistry in CMP has garnered increasing attention because of its potential to enhance the quality and efficiency of the GaN process.However,a considerable gap still exists in the comprehensive understanding of the specific photoelectrochemical(PEC)behavior of GaN.Here,we report the influence of the electrolyte on the PEC etching of GaN.Various acids and bases were tested,with their pH being carefully adjusted.The concentrations of the cations and anions were also examined.The results showed that photocorrosion/photoetching was more pronounced in sulfuric acid,phosphoric acid,and nitric acid environments than in alkaline environments,but it was less pronounced in hydrochloric acid.Furthermore,the effects of pH and anion concentration on photoetching were investigated,and the results revealed that pho-toetching in acidic environments weakened with increasing pH levels and diminished with increasing sulfate concentration.The underlying reasons contributing to this observation were explored.These findings provide ideas for improving the pho-toetching efficiency of GaN,thereby enriching the photoelectrochemical mechanical polishing(PECMP)technology of GaN.

Sponge-like nickel phosphide-carbon nanotube hybrid electrodes for efficient hydrogen evolution over a wide pH range

Cost-effective hydrogen production via electrolysis of water requires efficient and durable earth-abundant catalysts for the hydrogen evolution reaction （HER） over a wide pH range. Herein, we report sponge-like nickel phosphide- carbon nanotube （NixP/CNT） hybrid electrodes that were prepared by facile cyclic voltammetric deposition of amorphous NixP catalysts onto the three- dimensional （3D） porous CNT support. These compounds exhibit superior catalytic activity for sustained hydrogen evolution in acidic, neutral, and basic media. In particular, the NixP/CNT electrodes generate cathodic currents of 10 and 100 mA.cm-2 at overpotentials of 105 and 226 mV, respectively, in a 1 M phosphate buffer solution （pH = 6.5） with a Tafel slope of 100 mV.dec-1; the currents were stable for over 110 h without obvious decay. Our results suggest that the 3D porous CNT electrode supports could serve as a general platform for earth-abundant HER catalysts for the development of highly efficient electrodes for hydrogen production.

High mass-specific reactivity of a defect-enriched Ru electrocatalyst for hydrogen evolution in harsh alkaline and acidic media

A reasonable design strategy to improve the utilization of noble metal electrocatalysts for the hydrogen evolution reaction(HER)is crucial to simplify the process flow and accelerate the future renewable energy economy.Here,abundant defects were created on 2.4-nm Ru nanoparticles to achieve unprecedently high mass-specific reactivity in harsh acidic and alkaline electrolytes.The obtained defect-enriched Ru(DR-Ru)exhibits an ultrahigh HER turnover frequency of16.4 s^(-1)with a 100-mV overpotential in alkaline media,and it also retains an excellent value of 20.6 s^(-1)in acidic media;these results are superior to those reported for other Ru catalysts.Accordingly,a record-low loading of 2.5μg cm^(-2)for the DR-Ru catalysts and low overpotentials of 28.2 and 25.1 mV at10 mA cm^(-2)can be realized in alkaline and acidic media,respectively.Furthermore,the less coordinated Ru surface sites and partial lattice oxygen introduction weaken the bonding between H and DR-Ru catalysts,facilitate fast acidic HERkinetics and help dissociate the water molecule to overcome the major challenge of HER in alkaline electrolytes,leading to an activity comparable to that under acidic conditions.This result provides a guideline for defect engineering on noble metal nanocatalysts to effectively improve the utilization of the catalysts and optimize reactivities.

Insights into the efficiency and stability of Cu-based nanowires for electrocatalytic oxygen evolution

Copper oxide nanowires with varying oxidation states are prepared and their activity for water oxidation is studied. The nanowires with a CuO phase are found to be the most active, and their degree of crystallinity is important in achieving efficient water oxidation. For the crystalline CuO nanowires in a weakly basic Na2CO3 electrolyte, a Tafel slope of 41 mV/decade, an overpotential of approximately 500 mV at - 10 mA/crn2 （without compensation for the solution resistance）, and a faradaic efficiency of nearly 100% are obtained. This electrode maintains a stable current for over 15 lx The low overpotential of 500 mV at 10 mA/cm2, small Tafel slope, long-term stability, and low cost make CuO one of the most promising catalysts for water oxidation. Moreover, the evolution of the CuO nanowire morphology over time is studied by electron microscop）-revealing that the diffusion of Cu ions from the interior of the nanowires to their surface causes the aggregation of individual nanowires over time. However, despite this aggregation, the current density remains nearly constant, because the total electrochemically active surface area of CuO does not change.

Coordinately unsaturated nickel single atom electrocatalyst for efficient CO_(2)conversion

Single-atom catalysts(SACs)have shown unexpected catalytic activity due to their unique electronic structure and coordination environment.Nonetheless,the synthesis of an atomically precise low-coordination single-atom catalyst remains a grand challenge.Herein,we report a coordinately unsaturated Ni-N_(3)single-atom electrocatalyst using a metal-organic framework(MOF)derived N-C support with abundant exposed N for excellent electrochemical CO_(2)reduction.The obtained Ni-N_(3)/NC active site exhibited highly efficient CO_(2)-to-CO conversion with a Faradaic efficiency of 94.6%at the current density of 100 mA/cm^(2).In situ X-ray absorption spectroscopy(XAS)measurement suggested that the Ni atomic center with unsaturated coordination had the lower initial chemical state and higher charge transfer ability.In situ Fourier transform infrared(FT-IR)and theoretical calculation results revealed that the unsaturated catalytically active center could facilitate activation of CO_(2)and thus heighten CO_(2)electroreduction activity.These findings provided insights into the rational design of definitive coordination structure of SACs for boosting activity and selectivity.

Electrolyzer and Catalysts Design from Carbon Dioxide to Carbon Monoxide Electrochemical Reduction

Electrochemical CO_(2)reduction reaction(CO_(2)RR)has attracted considerable attention in the recent decade for its critical role in the storage of renewable energy and fulfilling of the carbon cycle,and catalysts with varying morphology and modification strategies have been studied to improve the CO_(2)RR activity and selectivity.However,most of the achievements are focused on preliminary reduction products such as CO and HCOOH.Development and research on electrochemical CO reduction reaction(CORR)are considered to be more promising to achieve multicarbon products and a better platform to understand the mechanism of C-C formation.In this review,we introduce the current achievements of CO_(2)RR and emphasize the potential of CORR.We provide a summary of how electrolysis environment,electrode substrates,and cell design affect the performance of CORR catalysts in order to offer a guideline of standard operating conditions for CORR research.The composition-structure-activity relationships for CORR catalysts studied in H-cells and gas-phase flow cells are separately analyzed to give a comprehensive understanding of the development of catalyst design.Finally,the reaction mechanism,latest progress,major challenges and potential opportunities of CORR are also analyzed to provide a critical overview for further performance improvement of CORR.

Recent advances in regulating the local environment of M-N_(4) structure for tailored chemical reactions

Single-atom catalysts(SACs)with M-N_(4)structure have drawn significant attention due to the facile preparation,maximum atom efficiency,unique electronic properties,uniform active sites,and excellent activity.Such catalysts integrated the merits of traditional homogeneous and heterogeneous catalysts effectively solve the cost,activity,and reuse problems.More importantly,the M-N_(4)structure is flexible and other species like atoms,groups,and particles can be added to precisely control the local environment of M-N_(4)to further improve the catalytic performance.Although unprecedented progress has been made,it remains difficulties in the rational design and controllable synthesis of a suitable SAC for a certain application.This review introduces the progress of M-N_(4)catalysts and summarizes the strategies to modulate the M-N_(4)structure,including changing the coordination number,tailoring the coordination structure,coordinating with groups,creating dual-atom catalysts(DACs),and coexisting of SAC with DAC and cluster.Special emphasis is placed on the preparation,structure characterization,and reaction mechanism of M-N_(4)-derived catalysts.Finally,the current challenges of these catalysts are also discussed to provide guidelines for the future design of efficient catalysts.