Stable overall water splitting in an asymmetric acid/ alkaline electrolyzer comprising a bipolar membrane sandwiched by bifunctional cobalt-nickel phosphide nanowire electrodes

Water splitting has been proposed to be a promising approach to producing clean hydrogen fuel.The two half-reactions of water splitting,that is,the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),take place kinetically fast in solutions with completely different pH values.Enabling HER and OER to simultaneously occur under kinetically favorable conditions while using exclusively low-cost,earth-abundant electrocatalysts is highly desirable but remains a challenge.Herein,we demonstrate that using a bipolar membrane(BPM)we can accomplish HER in a strongly acidic solution and OER in a strongly basic solution,with bifunctional self-supported cobaltnickel phosphide nanowire electrodes to catalyze both reactions.Such asymmetric acid/alkaline water electrolysis can be achieved at 1.567 V to deliver a current density of 10 mA/cm2 with ca.100%Faradaic efficiency.Moreover,using an“irregular”BPM with unintentional crossover the voltage needed to afford 10 mA/cm2 can be reduced to 0.847 V,due to the assistance of electrochemical neutralization between acid and alkaline.Furthermore,we show that BPM-based asymmetric water electrolysis can be accomplished in a circulated single-cell electrolyzer delivering 10 mA/cm2 at 1.550 V and splitting water very stably for at least 25 hours,and that water electrolysis is enabled by a solar panel operating at 0.908 V(@13 mA/cm2),using an“irregular”BPM.BPMbased asymmetric water electrolysis is a promising alternative to conventional proton and anion exchange membrane water electrolysis.

Non-peripherally octaalkyl-substituted nickel phthalocyanines used as non-dopant hole transport materials in perovskite solar cells

This report presents two non-perihperally octaalkyl-substituted nickel phthalocyanines(NiPcs),namely,NiEt2Pc and NiPr_(2)Pc,for use as dopant-free hole transport materials in perovskite solar cells(PSCs).The length extension of the alkyl chains from ethyl to propyl significantly tunes the NiPcs’energy levels,thus reducing charge carrier recombination at the perovskite/hole transport layer(HTL)interface and leading to higher open-circuit voltage(VOC)and short-circuit current density(JSC)observed for the NiPr_(2)Pc-based PSC.And higher charge carrier mobility,higher thin film crystallinity,and lower surface roughness of the NiPr_(2)Pc HTL compared with that of the NiEt2Pc one also lead to higher JSC and fill factor(FF)observed for the NiPr_(2)Pc-based device.Consequently,the NiPr_(2)Pc-based PSC exhibits a higher power conversion efficiency(PCE)of 14.07%than that of the NiEt2Pc-based device(8.63%).

Easy preparation of multifunctional ternary PdNiP/C catalysts toward enhanced small organic molecule electro-oxidation and hydrogen evolution reactions

The small organic molecule electro-oxidation(OMEO) and the hydrogen evolution(HER) are two important half-reactions in direct liquid fuel cells(DLFCs) and water electrolyzers,respectively,whose performance is largely hindered by the low activity and poor stability of electrocatalysts.Herein,we demonstrate that a simple phosphorization treatment of commercially available palladium-nickel(PdNi) catalysts results in multifunctional ternary palladium nickel phosphide(PdNiP) catalysts,which exhibit substantially enhanced electrocatalytic activity and stability for HER and OMEO of a number of molecules including formic acid,methanol,ethanol,and ethylene glycol,in acidic and/or alkaline media.The improved performance results from the modification of electronic structure of palladium and nickel by the introduced phosphorus and the enhanced corrosion resistance of PdNiP.The simple phosphorization approach reported here allows for mass production of highly-active OMEO and HER electrocatalysts,holding substantial promise for their large-scale application in direct liquid fuel cells and water electrolyzers.

Conformal and continuous deposition of bifunctional cobalt phosphide layers on p-silicon nanowire arrays for improved solar hydrogen evolution

Vertically aligned p-silicon nanowire （SiNW） arrays have been extensively investigated in recent years as promising photocathodes for solar-driven hydrogen evolution. However, the fabrication of SiNW photocathodes with both high photoelectrocatalytic activity and long-term operational stability using a simple and affordable approach is a challenging task. Herein, we report conformal and continuous deposition of a di-cobalt phosphide （C02P） layer on lithography- patterned highly ordered SiNW arrays via a cost-effective drop-casting method followed by a low-temperature phosphorization treatment. The as-deposited C02P layer consists of crystalline nanoparticles and has an intimate contact with SiNWs, forming a well-defined SiNW@Co2P core/shell nanostructure. The conformal and continuous Co2P layer functions as a highly efficient catalyst capable of substantially improving the photoelectrocatalytic activity for the hydrogen evolution reaction （HER） and effectively passivates the SiNWs to protect them from photo-oxidation, thus prolonging the lifetime of the electrode. As a consequence, the SiNW@Co2P photocathode with an optimized C02P layer thickness exhibits a high photocurrent density of -21.9 mA·cm^-2 at 0 V versus reversible hydrogen electrode and excellent operational stability up to 20 h for solar-driven hydrogen evolution, outperforming many nanostructured silicon photocathodes reported in the literature. The combination of passivation and catalytic functions in a single continuous layer represents a promising strategy for designing high-performance semiconductor photoelectrodes for use in solar-driven water splitting, which may simplify fabrication procedures and potentially reduce production costs.

Boosting acidic water oxidation performance by constructing arrays-like nanoporous Ir_(x)Ru_(1−x)O_(2) with abundant atomic steps

The fabrication of electrocatalysts with high activity and acid stability for acidic oxygen evolution reaction(OER)is an urgent need,yet extremely challenging.Here,we report the design and successful fabrication of a high performance self-supported cogwheel arrays-like nanoporous Ir_(x)Ru_(1−x)O_(2) catalyst with abundant atomic steps for acidic OER using a facile alloy-spinningelectrochemical activation method that allows large-scale fabrication.The obtained Ir_(x)Ru_(1−x)O_(2) catalysts merely need overpotentials of 211 and 295 mV to deliver catalytic current densities of 10 and 300 mA·cm^(−2) in 0.5 M H_(2)SO_(4),respectively,and can sustain constant OER electrolysis for at least 140 h at a high current density of 300 mA·cm^(−2).Further density functional theory(DFT)calculations uncover that such high intrinsic activities mainly originate from the largely exposed high-index atomic step planes,which markedly lower the limiting potential of the rate-determining step(RDS)of OER.These findings provide an insight into the exploration of high performance electrocatalysts,and open up an avenue for further developing the state-of-theart Ir and/or Ru-based catalysts for large-scale practical applications.

Plasma tailoring in WTe_(2)nanosheets for efficiently boosting hydrogen evolution reaction

2D transition metal dichalcogenides(TMDs)have been considered as promising non-precious electrocatalysts for the hydrogen evolution reaction(HER).However,their limited active sites and poor electric conductivity pose a significant hurdle to their HER performance,resulting in a large overpotential.Here,we report the defect engineering in ultrathin tungsten telluride(WTe_(2))nanosheets with semimetal nature to improve hydrogen evolution effectively.We find that the oxygen plasma etching imposes a cutting effect on WTe_(2)nanosheets,resulting in a large number of tungsten vacancies.Particularly,the sample after plasma treatment for 10 min shows a feather-like structure with an overpotential of 251m V at 10 m A/cm~2and a Tafel slope of 94 m V/dec,which is 4 times lower than the Tafel slope of pristine nanosheets.Further first-principles calculations shed light on the evolution of defect-rich WTe_(2)nanosheets and offer rational explanation to their superiority in efficient hydrogen evolution.

Oxygen electrochemistry in Li-O2 batteries probed by in situ surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy(SERS),as a nondestructive and ultrasensitive single molecular level characterization technique,is a powerful tool to deeply understand the interfacial electrochemistry reaction mechanism involved in energy conversion and storage,especially for oxygen electrochemistry in Li-O2 batteries with unrivaled theoretical energy density.SERS can provide precise spectroscopic identification of the reactants,intermediates and products at the electrode|electrolyte interfaces,independent of their physical states(solid and/or liquid)and crystallinity level.Furthermore,SERS’s power to resolve different isotopes can be exploited to identify the mass transport limitation and reactive sites of the passivated interface.In this review,the application of in situ SERS in studying the oxygen electrochemistry,specifically in aprotic Li-O2 batteries,is summarized.The ideas and concepts covered in this review are also extended to the perspectives of the spectroelectrochemistry in general aprotic metal-gas batteries.