Hot or Not? Reassessing Mechanisms of Photocurrent Generation in Plasmon-Enhanced Electrocatalysis.

It is now widely accepted that certain effects arising from localised surface plasmon resonance, such as enhanced electromagnetic fields, hot carriers, and thermal effects, can facilitate electrocatalytic processes. This newly emerging field of research is commonly referred to as plasmon-enhanced electrocatalysis (PEEC) and is attracting increasing interest from the research community, particularly regarding harnessing the high energy of hot carriers. However, this has led to a lack of critical analysis in the literature, where the participation of hot carriers is routinely claimed due to their perceived desirability, while the contribution of other effects is often not sufficiently investigated. As a result, correctly differentiating between the possible mechanisms at play has become a key point of contention. In this review, we specifically focus on the mechanisms behind photocurrents observed in PEEC and critically evaluate the possibility of alternative sources of current enhancement in the reported PEEC systems. Furthermore, we present guidelines for the best experimental practices and methods to distinguish between the various enhancement mechanisms in PEEC.

Phosphorus-Induced One-Step Synthesis of NiCo2S4 Electrode Material for Efficient Hydrazine-Assisted Hydrogen Production.

Rational control of the reaction parameters is highly important for synthesizing active electrocatalysts. NiCo2S4 is an excellent spinel-based electrocatalyst that is usually prepared through a two-step synthesis. Herein, a one-step hydrothermal route is reported to synthesize P-incorporated NiCo2S4. We discovered that the inclusion of P caused formation of the NiCo2S4 phase in a single step. Computational studies were performed to comprehend the mechanism of phase formation and to examine the energetics of lattice formation. Upon incorporation of the optimum amount of P, the stability of the NiCo2S4 lattice was found to increase steadily. In addition, the Bader charges on both the metal atoms Co and Ni in NiCo2S4 and P-incorporated NiCo2S4 were compared. The results show that replacing S with the optimal amount of P leads to a reduction in charge on both metal atoms, which can contribute to a more stable lattice formation. Further, the electrochemical performance of the as-synthesized materials was evaluated. Among the as-synthesized nickel cobalt sulfides, P-incorporated NiCo2S4 exhibits excellent activity toward hydrazine oxidation with an onset potential of 0.15 V vs RHE without the assistance of electrochemically active substrates like Ni or Co foam. In addition to the facile synthesis method, P-incorporated NiCo2S4 requires a very low cell voltage of 0.24 V to attain a current density of 10 mA cm-2 for hydrazine-assisted hydrogen production in a two-electrode cell. The free energy profile of the stepwise HzOR has been investigated in detail. The computational results suggested that HzOR on P-incorporated NiCo2S4 was more feasible than HzOR on NiCo2S4, and these findings corroborate the experimental evidence.

Nano-Impact Single-Entity Electrochemistry Enables Plasmon-Enhanced Electrocatalysis.

Plasmon-enhanced electrocatalysis (PEEC), based on a combination of localized surface plasmon resonance excitation and an electrochemical bias applied to a plasmonic material, can result in improved electrical-to-chemical energy conversion compared to conventional electrocatalysis. Here, we demonstrate the advantages of nano-impact single-entity electrochemistry (SEE) for investigating the intrinsic activity of plasmonic catalysts at the single-particle level using glucose electrooxidation and oxygen reduction on gold nanoparticles as model reactions. We show that in conventional ensemble measurements, plasmonic effects have minimal impact on photocurrents. We suggest that this is due to the continuous equilibration of the Fermi level (EF ) of the deposited gold nanoparticles with the EF of the working electrode, leading to fast neutralization of hot carriers by the measuring circuit. The photocurrents detected in the ensemble measurements are primarily caused by photo-induced heating of the supporting electrode material. In SEE, the EF of suspended gold nanoparticles is unaffected by the working electrode potential. As a result, plasmonic effects are the dominant source of photocurrents under SEE experimental conditions.

Ligand-Tuned Energetics for the Selective Synthesis of Ni2P and Ni12P5 Possessing Bifunctional Electrocatalytic Activity toward Hydrogen Evolution and Hydrazine Oxidation Reactions.

The occurrence of many phases and stoichiometries of nickel phosphides calls for the development of synthetic levers to selectively produce phases with purity. Herein, thiol (-SH) and carboxylate (-COO-) functional groups in ligands were found to effectively tune the energetics of nickel phosphide phases during hydrothermal synthesis. The initial kinetic product Ni2P transforms into thermodynamically stable Ni12P5 at longer reaction times. The binding of carboxylate onto Ni2P promotes this phase transformation to produce pure-phase Ni12P5 within 5 h compared to previous reports (∼48 h). Thiol-containing ligands inhibit this transformation process by providing higher stability to the Ni2P phase. Cysteine-capped Ni2P showed excellent geometric and intrinsic electrocatalytic activity toward both hydrogen evolution and hydrazine oxidation reactions under alkaline conditions. This bifunctional electrocatalytic nature enables cysteine-capped Ni2P to promote hydrazine-assisted hydrogen generation that requires lower energy (0.46 V to achieve 10 mA/cmgeo2) compared to the conventional overall water splitting (1.81 V to achieve 10 mA/cmgeo2) for hydrogen generation.

Design Principle of Monoclinic NiCo2Se4 and Co3Se4 Nanoparticles with Opposing Intrinsic and Geometric Electrocatalytic Activity toward the OER.

Despite predictions of high electrocatalytic OER activity by selenide-rich phases, such as NiCo2Se4 and Co3Se4, their synthesis through a wet-chemical route remains a challenge because of the high sensitivity of the various oxidation states of selenium to the reaction conditions. In this work, we have determined the contribution of individual reactants behind the maintenance of conducive solvothermal reaction conditions to produce phase-pure NiCo2Se4 and Co3Se4 from elemental selenium. The maintenance of reductive conditions throughout the reaction was found to be crucial for their synthesis, as a decrease in the reductive conditions over time was found to produce nickel/cobalt selenites as the primary product. Further, the reluctance of Ni(II) to oxidize into Ni(III) in comparison to the proneness of Co(II) to Co(III) oxidation was found to have a profound effect on the final product composition, as a deficiency of ions in the III oxidation state under nickel-rich reaction conditions hindered the formation of a monoclinic "Co3Se4-type" phase. Despite its lower intrinsic OER activity, Co3Se4 was found to show geometric performance on a par with NiCo2Se4 by virtue of its higher textural and microstructural properties.

Phosphorescent Trinuclear Pt-Ir-Pt Complexes: Insights into the Photophysical and Electrochemical Properties and Interaction with Guanine Nucleobase.

In this study we have analysed the comparative photophysical and electrochemical properties of two isomeric heterotrinuclear PtII -IrIII -PtII complexes 3 and 6 and the four corresponding intermediate isomeric homonuclear cyclometalated iridium(III) complexes 1, 2, 4 and 5. The isomerisation originates from positional differences in the formyl, di-2-picolylamine and Pt-di-2-picolylamine moieties appended to cyclometalated or ancillary ligands. The interaction of 5'-GMP with the trinuclear complexes 3 and 6 shows that platinum centres appended to the cyclometalated ligand in 3 facilitate the binding of two 5'-GMP units per PtII centre in preference to a single 5'-GMP unit per PtII centre as observed in 6. The 1:2 and 1:1 PtII -5'-GMP binding patterns probably arise from the convenient arrangements of the Pt-di-2-picolylamine units in different planes in complex 3, which is absent in complex 6.

Inception of Co3O4 as Microstructural Support to Promote Alkaline Oxygen Evolution Reaction for Co0.85Se/Co9Se8 Network.

Developing electrocatalysts with abundant active sites is a substantial challenge to reduce the overpotential requirement for the alkaline oxygen evolution reaction (OER). In this work, we have aimed to improve the catalytic activity of cobalt selenides by growing them over the self-supported Co3O4 microrods. Initially, Co3O4 microrods were synthesized through annealing of an as-prepared cobalt oxalate precursor. The subsequent selenization of Co3O4 resulted in the formation of a grainy rodlike Co3O4/Co0.85Se/Co9Se8 network. The structural and morphological analysis reveals the presence of Co3O4 even after the selenization treatment where the cobalt selenide nanograins are randomly covered over the Co3O4 support. The resultant electrode shows superior electrocatalytic activity toward OER in alkaline medium by delivering a benchmark current density of 10 mA/cm2geo at an overpotential of 330 mV. As a comparison, we have developed Co0.85Se/Co9Se8 under similar conditions and evaluated its OER activity. This material consumes an overpotential of 360 mV to deliver the benchmark current density, which signifies the role of the Co3O4 support to improve the electrocatalytic activity of Co0.85Se/Co9Se8. Despite having a low TOF value for Co3O4/Co0.85Se/Co9Se8 (0.0076 s-1) compared to Co0.85Se/Co9Se8 (0.0102 s-1), the improved catalytic activity of Co3O4/Co0.85Se/Co9Se8 is attributed to the presence of a higher number of active sites rather than the improved per site activity. This is further supported from the Cdl (double layer capacitance) measurements where Co3O4/Co0.85Se/Co9Se8 and Co0.85Se/Co9Se8 tender Cdl values of about 8.19 and 1.08 mF/cm2, respectively, after electrochemical precondition. As-prepared Co3O4/Co0.85Se/Co9Se8 also manifests rapid kinetics (low Tafel slope ∼ 91 mV/dec), long-term stability, low charge-transfer resistance, and 82% Faradaic efficiency for alkaline electrocatalysis (pH = 14). Furthermore, the proton reaction order (ρRHE) is found to be 0.65, indicating a proton decoupled electron transfer (PDET) mechanism for alkaline OER. Thus, the Co3O4 support helps in the exposure of more catalytic sites of Co0.85Se/Co9Se8 to deliver the improved catalytic activities in alkaline medium.

Design of Lanthanide-Doped Colloidal Nanocrystals: Applications as Phosphors, Sensors, and Photocatalysts.

The unique optical characteristics of lanthanides (Ln3+) such as high color purity, long excited-state lifetimes, less perturbation of excited states by the crystal field environment, and the easy spectral conversion of wavelengths through upconversion and downconversion processes have caught the attention of many scientists in the recent past. To broaden the scope of using these properties, it is important to make suitable Ln3+-doped materials, particularly in colloidal forms. In this feature article, we discuss the different synthesis strategies for making Ln3+-doped nanoparticles in colloidal forms, particularly ways of functionalizing hydrophobic surfaces to hydrophilic surfaces to enhance their dispersibility and luminescence in aqueous media. We have enumerated the various strategies and sensitizers utilized to increase the luminescence of the nanoparticles. Furthermore, the use of these colloidal nanoparticle systems in sensing application by the appropriate selection of capping ligands has been discussed. In addition, we have shown how the energy transfer efficiency from Ce3+ to Ln3+ ions can be utilized for the detection of toxic metal ions and small molecules. Finally, we discuss examples where the spectral conversion ability of these materials has been used in photocatalysis and solar cell applications.

Tuning the Energy Transfer Efficiency between Ce3+ and Ln3+ Ions (Ln=Tm, Sm, Tb, Dy) by Controlling the Crystal Phase of NaYF4 Nanocrystals.

NaYF4 is a superior host matrix to study the luminescence properties of lanthanide (Ln3+ ) ions. Ln3+ ions in hexagonal-phase NaYF4 (ß-phase) nanocrystals (NCs) exhibit strong luminescence via an upconversion process compared to cubic NaYF4 (α-phase) NCs. However, in Ce3+ /Ln3+ -doped NaYF4 NCs (Ln=Tm, Tb, Sm, Dy) the α-phase NaYF4 NCs shows strong luminescence compared to their counterpart ß-phase NCs despite the latter being much larger in size. This is attributed to comparatively large overlap between Ce3+ ions emission band with excited energy levels of those Ln3+ ions in α-phase compared to ß-phase NCs. This difference is attributed to different crystal-field splitting of Ce3+ ions 4f-5d band in different crystal environments of the α-phase (cubic crystal field environment) and ß-phase (trigonal prismatic with equatorials crystal field environment) NaYF4 NCs with respect to their barycenter. The enhanced luminescence from α-phase NaYF4 NCs is advantageous as they are prepared at a relatively lower temperature and shorter reaction times compared to ß-NaYF4 NCs.

A Highly Efficient UV-Vis-NIR Active Ln(3+)-Doped BiPO4/BiVO4 Nanocomposite for Photocatalysis Application.

In this Article, we report the synthesis of Ln(3+) (Yb(3+), Tm(3+))-doped BiPO4/BiVO4 nanocomposite photocatalyst that shows efficient photocatalytic activity under UV-visible-near-infrared (UV-vis-NIR) illumination. Incorporation of upconverting Ln(3+) ion pairs in BiPO4 nanocrystals resulted in strong emission in the visible region upon excitation with a NIR laser (980 nm). A composite of BiPO4 nanocrystals and vanadate was prepared by the addition of vanadate source to BiPO4 nanocrystals. In the nanocomposite, the strong blue emission from Tm(3+) ions via upconversion is nonradiatively transferred to BiVO4, resulting in the production of excitons. This in turn generates reactive oxygen species and efficiently degrades methylene blue dye in aqueous medium. The nanocomposite also shows high photocatalytic activity both under the visible region (0.010 min(-1)) and under the full solar spectrum (0.047 min(-1)). The results suggest that the photocatalytic activity of the nanocomposite under both NIR as well as full solar irradiation is better compared to other reported nanocomposite photocatalysts. The choice of BiPO4 as the matrix for Ln(3+) ions has been discussed in detail, as it plays an important role in the superior NIR photocatalytic activity of the nanocomposite photocatalyst.

Rejuvenating the Geometric Electrocatalytic OER Performance of Crystalline Co3 O4 by Microstructure Engineering with Sulfate.

Despite significant research on its electrocatalytic OER activity, the geometric performance of Co3 O4 has remained unsatisfactory compared to relatively amorphous Co-based materials. In particular, the activity of Co3 O4 prepared through annealing always gets inferior compared to its amorphous precursor. This demands the development of synthetic techniques to prepare Co3 O4 with superior activity as the unpredictable crystal structure of the amorphous materials makes it difficult to understand their structure-activity relationships despite higher geometric activity. In this article, we have shown that incorporation of sulfate in pre-annealed materials plays a pivotal role in boosting the OER activity of annealed Co3 O4 irrespective of the pre-annealed phase. In contrast to commonly used nitrate or carbonate that leaves the structure upon annealing and renders the resulting Co3 O4 with poor activity, sulfate remains in the annealed structure due to its thermal stability and causes a dramatic enhancement in the geometric electrocatalytic OER activity of resulting Co3 O4 compared to the pre-annealed phase. This was due to the "pore-alteration ability" and "crystallization hindrance effect" of sulfate ions that significantly alter the microstructure of the resulting Co3 O4 during annealing process by dramatically improving the surface area, pore size, and pore volume. Moreover, sulfate incorporation provided structures with considerably higher mesoporosity that is known to be conducive for reactant and product diffusion within the network. The improved textural properties led to better exposure of the catalytic centres to the electrolyte leading to higher geometric OER activity despite identical intrinsic activity of both sulfate free and incorporated Co3 O4 as confirmed from their specific activities. Further, the Co3 O4 synthesized by annealing sulfate incorporated precursor was found to be rich with oxygen defects that are known to increase the potency of a material towards electrocatalytic OER. The sulfate ions also etched out in the electrolyte during electrocatalysis leading to complete unblocking of the pores thereby helping in sustaining the high geometric OER activity. To our knowledge, this is the first report where the geometric electrocatalytic OER activity of an annealed Co3 O4 is significantly better compared to its pre-annealed phase and is in fact comparable to the activity of amorphous Co-hydroxide based compounds.

Nickel-cobalt oxalate as an efficient non-precious electrocatalyst for an improved alkaline oxygen evolution reaction.

The quest for developing next-generation non-precious electrocatalysts has risen in recent times. Herein, we have designed and developed a low cost electrocatalyst by a ligand-assisted synthetic strategy in an aqueous medium. An oxalate ligand-assisted non-oxide electrocatalyst was developed by a simple wet-chemical technique for alkaline water oxidation application. The synthetic parameters for the preparation of nickel-cobalt oxalate (Ni2.5Co5C2O4) were optimized, such as the metal precursor (Ni/Co) ratio, oxalic acid amount, reaction temperature, and time. Microstructural analysis revealed a mesoporous block-like architecture for nickel-cobalt oxalate (Ni2.5Co5C2O4). The required overpotential of Ni2.5Co5C2O4 for the alkaline oxygen evolution reaction (OER) was found to be 330 mV for achieving 10 mA cmgeo -2, which is superior to that of NiC2O4, CoC2O4, NiCo2O4 and the state-of-the-art RuO2. The splendid performance of Ni2.5Co5C2O4 was further verified by its low charge transfer resistance, impressive stability performance, and 87% faradaic efficiency in alkaline medium (pH = 14). The improved electrochemical activity was further attributed to double layer capacitance (C dl), which indefinitely divulged the inferiority of NiCo2O4 compared to Ni2.5Co5C2O4 for the alkaline oxygen evolution reaction (OER). The obtained proton reaction order (ρ RHE) was about 0.80, thus indicating the proton decoupled electron transfer (PDET) mechanism for OER in alkaline medium. Post-catalytic investigation revealed the formation of a flake-like porous nanostructure, indicating distinct transformation in morphology during the alkaline OER process. Further, XPS analysis demonstrated complete oxidation of Ni2+ and Co2+ centres into Ni3+ and Co3+, respectively under high oxidation potential, thereby indicating active site formation throughout the microstructural network. Additionally, from BET-normalised LSV investigation, the intrinsic activity of Ni2.5Co5C2O4 was also found to be higher than that of NiCo2O4. Finally, Ni2.5Co5C2O4 delivered a TOF value of around 3.28 × 10-3 s-1, which is 5.56 fold that of NiCo2O4 for the alkaline OER process. This report highlights the unique benefit of Ni2.5Co5C2O4 over NiCo2O4 for the alkaline OER. The structure-catalytic property relationship was further elucidated using density functional theory (DFT) study. To the best of our knowledge, nickel-cobalt oxalate (Ni2.5Co5C2O4) was introduced for the first time as a non-precious non-oxide electrocatalyst for alkaline OER application.

Ethylene glycol-mediated one-pot synthesis of Fe incorporated α-Ni(OH)2 nanosheets with enhanced intrinsic electrocatalytic activity and long-term stability for alkaline water oxidation.

Sustainable electrocatalytic water splitting stipulates the development of cheap, efficient and stable electrocatalysts to promote comparatively sluggish oxygen evolution reaction. We have synthesized iron-incorporated pure phase α-nickel hydroxide, Ni0.8Fe0.2(OH)2 electrocatalyst utilizing N,N,N',N'-Tetramethylethane-1,2-diamine (TMEDA) and ethylene glycol (EG) following a simple one-pot synthesis process. PXRD and FTIR data suggest that the intercalation of EG in the interlayer spacing promotes amorphousness of the material. FESEM and TEM analyses suggest that the catalyst possesses hierarchical sheet-like morphology and BET measurements indicated the surface area of 50 m2 g-1 with high mesoporosity. Electrochemical studies suggest that Ni0.8Fe0.2(OH)2 prepared using water-EG mixture is the most efficient electrocatalyst for OER activity as it requires only 258 mV overpotential (considering backward LSV) on a glassy carbon electrode to achieve the benchmark current density of 10 mA cm-2geo. Additionally, the catalyst shows remarkable long-term stability for up to 7 days. The efficiency of Ni0.8Fe0.2(OH)2 electrocatalyst is reflected in its low Tafel slope (43 mV dec-1) and high OER faradaic efficiency (93%). The enhanced activity is attributed to the increase in the interlayer spacing due to the intercalation of EG into the material, which facilitates the transport of ions during the OER process. The overall improved catalytic property is due to the enhanced ionic mobility, controllable textural property, higher per-site activity and increased conductivity for the Ni0.8Fe0.2(OH)2 catalytic network.

Prudent electrochemical pretreatment to promote the OER by catalytically inert "Iron incorporated metallic Ni nanowires" synthesized via the "non-classical" growth mechanism.

This study provides new insight towards the non-classical "amorphous to crystalline" growth mechanism for metal nanowire synthesis and reports an electrochemical strategy to activate inactive materials into efficient electrocatalysts for the OER. Despite considerable research on transition metal oxides/hydroxides, especially NiFe based hydroxides as OER electrocatalysts, poor conductivity of these materials plagues their catalytic efficiency. In contrast, lack of catalytic centers hinders the OER performance of conductive metals. Herein, we devised a suitable precondition strategy to transform only the surface of conductive metallic Ni nanowires into active catalytic centers. The resulting material with intimate contact between the electrically conductive core and electrocatalytically active surface showed promising "specific" and "geometric" electrocatalytic activity towards the alkaline OER at different pH. Upon iron incorporation, the Fe centers incorporated at the surface as well as in the bulk of the nanowires were found to further boost the OER activity of these materials. A one-pot strategy was adopted to produce iron free/incorporated Ni nanowires covered with nano-spikes. Growth analysis revealed a unique "non-classical amorphous-to-crystalline transformation" to be responsible for the formation of metallic nanowires.

Inception of molybdate as a "pore forming additive" to enhance the bifunctional electrocatalytic activity of nickel and cobalt based mixed hydroxides for overall water splitting.

Development of low-cost transition metal based electrocatalysts on inexpensive substrates for overall water splitting is essential to meet the future energy storage demand. In this article, we have synthesized a molybdate incorporated nickel cobalt hydroxide material on Cu mesh with nickel : cobalt : molybdenum in a 13.25 : 21.42 : 1 ratio and the electrode has shown excellent bifunctional electrocatalytic activity as it demonstrates overpotentials as low as 290 mV and 125 mV to reach 10 mA cm-2geo for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively (after both iR and capacitance correction). Control studies with fourteen other nickel-cobalt based hydroxides and rigorous post-catalytic analysis suggested that though molybdate was not the active catalytic centre, it played a pivotal role in enhancing the activity of the material as - (i) it significantly improved the surface area and porosity of the as-synthesized material and (ii) owing to its continuous etching during electrochemical testing, it was found to increase the accessibility of electrochemically active catalytic sites lying in the bulk. Thus, molybdate acts as a "pore forming additive" during both synthesis and electrochemical treatment. Furthermore, the combination of nickel and molybdate helped in the formation of a 2D-sheet like morphology which in turn improves accessibility to catalytically active centres. In addition, the Cu mesh substrate notably lowers the charge transfer resistance. To the best of our knowledge, this is the first ever report of molybdate as a "pore forming additive" and will enthuse the designing of electrocatalytic materials with enhanced performance based on this strategy.

Effect of Intrinsic Properties of Anions on the Electrocatalytic Activity of NiCo2O4 and NiCo2O x S4-x Grown by Chemical Bath Deposition.

Electrochemical water (H2O) splitting is one of the most promising technologies for energy storage by hydrogen (H2) generation but suffers from the requirement of high overpotential in the anodic half-reaction (oxygen evolution), which is a four-electron process. Though transition-metal oxides and oxysulfides are increasingly researched and used as oxygen evolution electrocatalysts, the bases of their differential activities are not properly understood. In this article, we have synthesized NiCo2O4 and NiCo2O x S4-x by a chemical bath deposition technique, and the latter has shown better oxygen evolution performance, both in terms of stability and activity, under alkaline conditions. Comprehensive analysis through time-dependent cyclic voltammetry, microscopy, and elemental analysis reveal that the higher activity of NiCo2O x S4-x may be attributed to the lower metal-sulfur bond energy that facilitates the activation process to form the active metal hydroxide/oxyhydroxide species, higher electrochemically active surface area, higher pore diameter and rugged morphology that prevents corrosion. This work provides significant insights on the advantages of sulfur-containing materials as electrochemical precatalysts over their oxide counterparts for oxygen evolution reaction.

Near-infrared light triggered superior photocatalytic activity from MoS2-NaYF4:Yb(3+)/Er(3+) nanocomposites.

A near infrared (NIR) responsive photocatalyst, composed of a narrow band gap semiconductor (i.e. MoS2) and an optical material possessing upconverting ability (i.e. NaYF4:Yb(3+)/Er(3+)) has been successfully prepared via a simple hydrothermal method. The latter has the ability to convert NIR light into visible light while the MoS2 uses the light to degrade organic pollutants. Upon near infrared (NIR) excitation of the MoS2-NaYF4:Yb(3+)/Er(3+) nanocomposites, the energy of the strong green and the red emissions along with the weak violet emissions from the NaYF4:Yb(3+)/Er(3+) nanocrystals (NCs) is transferred to MoS2. This results in enhanced NIR light triggered photocatalytic performance, as verified by studying the degradation of Rhodamine B (RhB) dye under 980 nm laser excitation. The strong photocatalytic activity of MoS2-NaYF4:Yb(3+)/Er(3+) composites is attributed to the layered nature of the photocatalyst which leads to the efficient separation of photogenerated carriers (electron-hole pairs) and excellent upconversion properties of NaYF4:Yb(3+)/Er(3+) NCs. The study also shows the importance of the composite formation, as the physical mixture leads to only very low photocatalytic activity. Our results can be helpful in the structural design and development of high-performance photocatalysts.