Concentration Of Surface Hydroxyl Groups Research Articles

Kinetic Study of the Oxygen Reduction Reaction on α-Ni(OH)2 and α-Ni(OH)2 Supported on Graphene Oxide

The kinetics of the oxygen reduction reaction on α-Ni(OH)2 and α-Ni(OH)2 supported on graphene oxide (α-Ni(OH)2/GO) were investigated using rotating disk linear sweep voltammetry in alkaline solutions of varying oxygen and hydroxyl concentrations. Over the full hydroxyl concentration range (0.05 M to 0.5M), α-Ni(OH)2/GO displayed higher activity than unsupported α-Ni(OH)2. The electron transfer numbers were 2.9 ± 0.2 for α-Ni(OH)2, 3.4 ± 0.1 for α-Ni(OH)2/GO at low [OH−], and 3.8–3.9 for α-Ni(OH)2/GO at high [OH−]. Compared to α-Ni(OH)2, α-Ni(OH)2/GO displayed higher chemical reaction rate constants and higher electron transfer rate constants. These differences suggest that the synergy between the α-Ni(OH)2 catalyst and the graphene oxide support is related to increases in both the speed of the rate determining chemical step and the facility for electron transfer. The order of reaction with respect to oxygen was ∼1 for α-Ni(OH)2 and α-Ni(OH)2/GO. The order of reaction with respect to hydroxyl was ∼0 for α-Ni(OH)2 and α-Ni(OH)2/GO. The first order reaction with respect to oxygen is precedented, but the zero reaction order with respect to hydroxyl is particular to the α-Ni(OH)2 catalysts. The zero reaction order is explained by possible decoupling of solution and catalyst surface hydroxyl concentrations.

Mechanistic aspects of formation of sintering-resistant palladium nanoparticles over SiO2 prepared using Pd(acac)2 as precursor

SiO2-supported Pd(acac)2 was prepared by impregnation of the support material in Pd(acac)2/acetylacetone solution. Interaction between Pd(acac)2 and SiO2 surface and thermal decomposition of the Pd(acac)2/SiO2 sample in air were characterized in detail by a variety of techniques including thermogravimetric-mass spectroscopy analyses, in situ infrared spectroscopy, X-ray photoelectron spectroscopy, in situ X-ray powder diffraction, and transmission electron microscope. The results indicate that the surface silanol groups on SiO2 acted as the centers of interaction with Pd(acac)2 molecules when SiO2 was impregnated in the Pd(acac)2 solution, leading to the formation of hydrogen bonded Pd(acac)2 on SiO2 surface. Concentration of silanol groups on SiO2 surface has a direct impact on the dispersion of Pd(acac)2 on SiO2 surface. In the Pd(acac)2/SiO2 sample prepared with a fully hydroxylated silica, no multiple layer Pd(acac)2 species was detected on SiO2 surface when Pd loading was below 8wt%. When a silica supported Pd(acac)2 sample was heated to ∼200°C in air, the single layer of Pd(acac)2 species on SiO2 surface decomposed into the metallic Pd nanoparticles with an average size of about 2.8nm. The resulting Pd nanoparticles demonstrated superior stability against sintering at high temperature. No significant aggregation of the Pd nanoparticles was observed when the sample was heated to 800°C in air or to 600°C in a mixture of H2/Ar=5/95 (volume ratio). In the Pd(acac)2/SiO2 samples with Pd loadings higher than 9wt% or the samples prepared with a silica of low concentration of surface hydroxyl groups, however, multiple layers of Pd(acac)2 could also form on the SiO2 surface, because there were no enough surface OH sites to allow all Pd(acac)2 molecules to “fit” into the single layer. Decomposition of multiple layer Pd(acac)2 species in air at elevated temperature resulted in the formation of large Pd particles on SiO2.

Enhanced arsenate removal performance of nanostructured goethite with high content of surface hydroxyl groups

Goethite (α-FeOOH) with high content of surface hydroxyl groups was synthesized by using a simple sodium dodecyl sulfate (SDS) assisted solution method. The presence of SDS can increase the surface area and the contents of surface hydroxyl groups. The adsorption properties towards arsenate (As(V)) ions were investigated, including adsorption kinetics, adsorption isotherm, influences of pH and coexisting anions, and regeneration of the adsorbent. The maximal adsorption capacity was 60.6mgg−1 at pH 7.0, which is about three times larger than the ones synthesized in pure water, and also is favorable compared to those reported in the literature using other adsorbents. The coexisting of phosphate and carbonate inhibited the As(V) removal especially at high concentrations. The as-prepared α-FeOOH could be readily regenerated using NaOH solution and be repeatedly used in the field of water purification. In addition, the removal mechanism was revealed by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and the zeta potential study. The point of zero charge (pHPZC) of the α-FeOOH is 6.35. At high solution pH, the ion-exchange between the surface hydroxyl groups and As(V) ions dominates in the adsorption of As(V). Around the pHPZC, the hydrogen bonding also contributes to the As(V) removal. When the solution pH is lower than pHPZC, the electrostatic attraction plays key roles in As(V) removal.

Influence of surface morphology and surface area on release behavior of hydrogen isotopes in LiNbO3

Surface processes have profound influence on tritium release behavior in ceramic breeder materials. In this paper, the release behavior of hydrogen isotopes in LiNbO3 is studied by thermal desorption spectroscopy (TDS) with focusing on the influence of the surface morphology and surface area. It is found that the amount of surface hydroxyl groups is proportional to the specific surface area and can be decreased by smoothing the surface roughness through heating pretreatment at high temperatures. The isotope exchange reaction between the surface hydroxyl groups and water molecules residue in the system is discussed and turns out to proceed fast. The release behavior of hydrogen isotopes in LiNbO3 is compared with that in Li2TiO3 studied in our previous work. It reveals that LiNbO3 and Li2TiO3 have similar surface environment and similar concentration of surface hydroxyl groups with the level of 1020m−2. The formation mechanism of hydroxyl groups on the surface is discussed and a model to explain the experimental observations is proposed.

Pr, N, and P tri-doped anatase TiO2 nanosheets with enhanced photocatalytic activity under sunlight

Pr, N, and P tri-doped anatase TiO2 nanosheets (PrNPTO) were synthesized by a combined sol-gel solvothermal method and characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption, X-ray photoelectron spectroscopy, UV-vis absorbance spectroscopy, and photoluminescence spectroscopy. When the Pr-doping concentration was 1.75 wt% and calcination temperature employed was 550 °C, the resulting PrNPTO showed the highest photoactivity towards the degradation of methylene blue under visible and UV light irradiation. PrNPTO also displayed superior photoactivity towards the degradation of 4-chlorophenol under sunlight (kapp = 3.90 × 10−2 min−1) over the non-doped, single-doped, and co-doped samples, and P25 TiO2 (kapp = 1.17 × 10−2 min−1). The high photoactivity of PrNPTO was attributed to the increased UV and visible light absorption properties, reduced recombination of photogenerated carriers, increased surface hydroxyl content, and improved surface textural properties. PrNPTO was highly efficient and stable under simulated sunlight irradiation, which are essential attributes for practical application in environment-related remediation schemes.

Synthesis of micro-sized hierarchical TiO2 particles of nano-scale effectiveness and their photocatalytic activities at various surface hydroxyl concentrations

The 3-dimensional hierarchical TiO2 particles of micro-sized diameter were synthesized through modified sol–gel process with polyethylene glycol (PEG) as a structure-controlling agent. The anatase crystal structure was obtained after calcination at 450 °C. The size and specific surface area of particles were 1.0–1.8 μm and 96.85 m2 g−1, respectively. The specific surface area of the TiO2 particles corresponded to that of the spherical nanoparticles with average size of 15.9 nm. Although the size of synthesized TiO2 was micro-scale, they had the specific surface area similar to that of nano-scale particles due to the effect of PEG on the formation of particles. Subsequently, the surface modification with various concentration of ammonia solution was carried out for the preparation of hydroxyl-rich TiO2 particles at surfaces. As the concentration of ammonia solution was increased, the amount of chemically adsorbed hydroxyl groups on the TiO2 surface was increased. As an application of prepared TiO2 for water treatment, their catalytic performances for the degradation of methylene blue (MB) were examined by using UV–Vis spectrophotometer with the assistance of UV lamp. After hydroxylation treatment, the micro-sized TiO2 particles showed the higher performance of MB degradation than that of nano-sized P25 particles because of their large specific surface area and hydroxyl-rich surface.

Hydrothermal synthesis of high-efficiency Pr, N, P-tridoped TiO2 from TiCl4 hydrolysis and mechanism of its enhanced photoactivity

A hydrothermal method without post-calcination was successfully developed to obtain high-efficiency Pr, N, P-tridoped anatase-TiO2 (PrNPTO) nano-photocatalyst based on TiCl4 hydrolysis in aqueous solution. The samples were characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption–desorption isotherm, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, thermogravimetry and differential thermoanalysis, UV–vis absorbance spectroscopy, and photoluminescence spectroscopy measurements. Results showed that among as-synthesized undoped and doped samples, PrNPTO presented the highest photoactivity for 4-chlorophenol (4-CP) degradation under simulated sunlight irradiation (Kapp=0.0603min−1), which was 5.15 times that of commercial P25 TiO2 (Kapp=0.0117min−1). TOC removal rate for 4-CP solution (20mgL−1) in the presence of PrNPTO (0.8gL−1) reached 76.9% after 120min irradiation, indicating that 4-CP was mineralized efficiently. Radical scavenging experiments indicated that OH in the solution was main reactive species, but photogenerated electrons also played a minor role by finally transformed OH. Enhanced photoactivity of PrNPTO was attributed to the increased UV light absorption, reduced photogenerated e−/h+ recombination, higher surface hydroxyl content, as well as improved surface textural properties. PrNPTO was reused many times without obvious diminution of photoactivity, which extends the practical application of TiO2.

Maximizing the catalytic function of hydrogen spillover in platinum-encapsulated aluminosilicates with controlled nanostructures

Hydrogen spillover has been studied for several decades, but its nature, catalytic functions and even its existence remain topics of vigorous debate. This is a consequence of the lack of model catalysts that can provide direct evidences of the existence of hydrogen spillover and simplify the catalytic interpretation. Here we use platinum encapsulated in a dense aluminosilicate matrix with controlled diffusional properties and surface hydroxyl concentrations to elucidate the catalytic functions of hydrogen spillover. The catalytic investigation and theoretical modelling show that surface hydroxyls, presumably Brønsted acids, are crucial for utilizing the catalytic functions of hydrogen spillover on the aluminosilicate surface. The catalysts with optimized nanostructure show remarkable activities in hydro-/dehydrogenation, but virtually no activity for hydrogenolysis. This distinct chemoselectivity may be beneficial in industrially important hydroconversions such as propane dehydrogenation to propylene because the undesired hydrogenolysis pathway producing light hydrocarbons of low value (methane and ethane) is greatly suppressed.

Dehydroxylation action on surface of TiO2 films restrained by nitrogen carrier gas during atomic layer deposition process

A strong influence of nitrogen gas on the content of surface hydroxyl groups of TiO2 films by atomic layer deposition (ALD) was investigated by X-ray photoelectron spectroscopy (XPS), contact angle measuring system, and UV–Vis spectrophotometer. XPS spectra of O 1s indicate that the content of surface hydroxyl groups is varied when using N2 as carrier gas. The results of water contact angles and optical reflection spectra show that the content variation of surface hydroxyl groups influences the wetting properties and optical reflectivity of TiO2 films. A surface reaction model is suggested to explain the ALD reaction process using N2 as carrier gas.

Thermal decomposition of ammonium perchlorate in the presence of Al(OH)3·Cr(OH)3 nanoparticles

An Al(OH)3·Cr(OH)3 nanoparticle preparation procedure and its catalytic effect and mechanism on thermal decomposition of ammonium perchlorate (AP) were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis and differential scanning calorimetry (TG-DSC), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis and mass spectroscopy (TG-MS). In the preparation procedure, TEM, SAED, and FT-IR showed that the Al(OH)3·Cr(OH)3 particles were amorphous particles with dimensions in the nanometer size regime containing a large amount of surface hydroxyl under the controllable preparation conditions. When the Al(OH)3·Cr(OH)3 nanoparticles were used as additives for the thermal decomposition of AP, the TG-DSC results showed that the addition of Al(OH)3·Cr(OH)3 nanoparticles to AP remarkably decreased the onset temperature of AP decomposition from approximately 450°C to 245°C. The FT-IR, RS and XPS results confirmed that the surface hydroxyl content of the Al(OH)3·Cr(OH)3 nanoparticles decreased from 67.94% to 63.65%, and Al(OH)3·Cr(OH)3 nanoparticles were limitedly transformed from amorphous to crystalline after used as additives for the thermal decomposition of AP. Such behavior of Al(OH)3·Cr(OH)3 nanoparticles promoted the oxidation of NH3 of AP to decompose to N2O first, as indicated by the TG-MS results, accelerating the AP thermal decomposition.

Amine‐functionalization of the nanotitanate ETS‐2

A series of nonporous, amine‐functionalized sodium titanates was prepared and the thermal and adsorptive behavior of the samples were characterized. Engelhard titanosilicate 2 was chosen as a substrate for its high surface area (∼300 m2/g), native surface hydroxyl concentration, and lack of microporosity; eliminating the risk of fouling the adsorbent under certain process conditions. Aminosilanes containing a single (N1), two (N2), and three (N3) amine groups were chemically grafted to the surface of the substrate and the adsorption capacity for CO2 measured through thermogravimetry‐mass spectroscopy (TG‐MS) desorption, volumetric adsorption, and gravimetric adsorption/desorption cycling. The N3 sample displayed complete monolayer coverage and was capable of adsorbing five times as much atmospheric CO2 as the N1 sample. Testing under anhydrous conditions only engages the primary amine on the tether and the data consistently suggests a correlation between amine utilization and the proportion of monolayer coverage for these adsorbents. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4727–4734, 2013

Surface fractal dimensions and textural properties of mesoporous alkaline-earth hydroxyapatites

This work examines the surface fractal dimensions (Df) and textural properties of three different alkaline-earth hydroxyapatites. Calcium, strontium and barium hydroxyapatite compounds were successfully synthesized via chemical precipitation method and characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometry, Fourier transform infrared spectroscopy, and N2-physisorption measurements. Surface fractal dimensions were determined using single N2-adsorption/desorption isotherms method to quantify the irregular surface of as-prepared compounds. The obtained materials were also characterized through their surface hydroxyl group content, determined by the mass titration method. It was found that the Df values for the three materials covered the range of 0.77±0.04–2.33±0.11; these results indicated that the materials tend to have smooth surfaces, except the irregular surface of barium hydroxyapatite. Moreover, regarding the synthesized calcium hydroxyapatite exhibited better textural properties compared with the synthesized strontium and barium hydroxyapatites for adsorbent purposes. However, barium hydroxyapatite shows irregular surface, indicating a high population of active sites across the surface, in comparison with the others studied hydroxyapatites. Finally, the results showed a linear correlation between the surface hydroxyl group content at the external surface of materials and their surface fractal dimensions.

Removal of Pb(II) from aqueous solution by hydrous manganese dioxide: Adsorption behavior and mechanism

Hydrous manganese dioxide (HMO) synthesized by redox of potassium permanganate and hydrogen peroxide was used as an adsorbent for Pb(II) removal. The specific surface area, pore volume and BJH pore diameter of the HMO were 79.31 m2/g, 0.07 cm3/g and 3.38 nm, respectively. The adsorption equilibrium at 298 K could be well described by the Langmuir isotherm equation with qmax value of 352.55 mg/g. The negative values of ΔG and the positive values of ΔH and ΔS indicated the adsorption process was spontaneous and endothermic. The pseudo second-order equation could best fit the adsorption data. The value of the calculated activation energy for Pb(II) adsorption onto the HMO was 38.23 kJ/mol. The uptake of Pb(II) by HMO was correlated with increasing surface hydroxyl group content and the main adsorbed speciation was PbOH+. The final chemical state of Pb(II) on the surface of HMO was similar to PbO. HMO was a promising candidate for Pb(II) removal from aqueous solution.

Small molecule – Silica interactions in porous silica structures

A series of porous silica frameworks with different pore sizes (SSZ-59, MCM-41 and SBA-15) was studied by immersion calorimetry in various solutions (water, ethanol, triethylamine, NaCl brine and Na2CO3/NaHCO3 buffer) at 25°C to determine the interaction energies between inorganic silica frameworks and various small molecules which may be of importance in the context of CO2 sequestration, carbonate mineralization, and environmental remediation. The enthalpies of immersion for the calcined porous silica samples range from −0.7 to −9.6kJ per mole of SiO2 in water, −3.4 to −10.5kJ per mole of SiO2 in ethanol, −5.7 to −15.1kJ per mole of SiO2 in triethylamine, −1.5 to −11.4kJ per mole of SiO2 in NaCl brine (1M) and −0.5 to −8.0kJ per mole of SiO2 in a Na2CO3/NaHCO3 buffer solution (1M). The enthalpies of interaction between porous silicas and water, ethanol and triethylamine vary from −0.3 to −2.3kJ per mole of H2O, from −49.1 to −62.5kJ per mole of ethanol and from −65.5 to −95.6kJ per mole of triethylamine. The enthalpies of interaction suggest that guest–host interactions in silica-based porous media are governed both by pore size and concentration of surface hydroxyl groups. The generally hydrophobic surfaces of porous silica materials bond more strongly to organic molecules (ethanol and triethylamine) than to aqueous solutions and the energetics of such functionalized organic – rich silica surfaces could play a significant role in geologic CO2 sequestration, enhanced oil recovery, and geochemistry in low-temperature diagenetic and sedimentary environments.

Synthesis of monodispersed α-FeOOH nanorods with a high content of surface hydroxyl groups and enhanced ion-exchange properties towards As(v)

Monodispersed α-FeOOH nanorods, with a high content of surface hydroxyl groups, were synthesized using a simple solution method at room temperature. The obtained α-FeOOH nanorods were characterized by field emission scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, nitrogen adsorption–desorption isotherms and X-ray diffraction. The presence of cetyltrimethylammonium bromide (CTAB) successfully avoids the congregation of the α-FeOOH nanorods, which resulted in the formation of the monodispersed α-FeOOH nanorods and the increase of the surface hydroxyl groups. The adsorption properties of the nanorods towards toxic As(V) ions were investigated. The results suggest that the adsorption properties of the monodispersed α-FeOOH nanorods were also improved compared with the congregated ones synthesized without CTAB or surfactant instead of pure water. The enhanced adsorption properties were attributed to the high content of the surface hydroxyl groups, which were revealed by X-ray photoelectron spectrometer and Fourier transform infrared absorption spectroscopy.

Hierarchically mesostructured TiO2/graphitic carbon composite as a new efficient photocatalyst for the reduction of CO2 under simulated solar irradiation

A hierarchically mesostructured TiO2/graphitic carbon composite photocatalyst with a high content of nanocrystalline TiO2 was prepared using a simple one-step nanocasting route. X-ray diffraction, thermogravimetric analysis, nitrogen adsorption–desorption, transmission electron microscopy and X-ray photoelectron spectroscopy were used to characterize this photocatalyst. It was observed that the coexistence of silica and graphitic carbon during the high temperature treatment stabilized the crystalline phase and the size of the anatase TiO2 nanocrystals (5–7 nm in diameter), which were uniformly dispersed in the graphitic carbon matrix after silica removal. The obtained hierarchically mesostructured TiO2/graphitic carbon composite photocatalyst with a high specific surface area and a high surface concentration of hydroxyl groups exhibited considerably higher activity in the photocatalytic reduction of CO2 with H2O under simulated solar irradiation compared to mesostructured anatase TiO2 prepared using a sol–gel method.

Probing substrate effects on relaxation dynamics of ultrathin poly(vinyl acetate) films by dynamic wetting of water droplets on their surfaces

The dynamic wetting of water droplets on ultrathin poly(vinyl acetate) (PVAc) films supported by substrates with tunable surface hydroxyl group content was investigated at room temperature. The jumping angle of water droplets on the ultrathin PVAc films decreased with increasing hydroxyl content on the substrate surface, while a smooth evolution of the water droplet contacting line emerged for the film supported by a substrate with 100% hydroxyl groups. The critical thickness of ultrathin PAVc films, through which the interfacial effect from substrate chemistry on the dynamic wetting of water droplets on their surfaces will disappear, was measured by this novel method and the results showed that the critical thickness increased from ∼35 nm to ∼75 nm with increasing hydroxyl content from 41% to 100% on the substrate. This relationship between critical thickness and hydroxyl content was attributed to the intensities of the hydrogen bonds, resulting in lower chain mobility at the interface and a higher elastic modulus of the whole ultrathin film. This study demonstrates that the dynamic wetting of a liquid droplet on ultrathin polymer films is very sensitive and effective to access their mechanical properties, relaxation behavior and those properties affected by the substrate surface chemistry.

Removal of cationic Rhodamine-B dye using nano-titania with anatase crystalline structure and kinetic analysis of the photocatalytic reaction

Heterogeneous photocatalytic removal of Rhodamine-B (RhB) dye from liquid phase was done using anatase-phase nanocrystalline TiO2 synthesized via a modified sol-gel process. The anatase-phase nanocrystalline TiO2 was characterized using various analytical techniques including XRD, UV-vis DRS, PL, and FTIR to investigate its phase composition and structure, nanocrystalline size, band gap energy, photoluminescence and surface properties of the prepared systems. The photocatalytic discoloration efficiency of anatase-phase nanocrystalline titania was investigated by monitoring the decomposition of RhB dye as target compounds in an aqueous solution. The results showed that the as-prepared anatase-phase nanocrystalline TiO2 was excellent for degradation of RhB molecule, and the crystallite size, excitonic PL and surface hydroxyl content have intimate relationship with the decomposition efficiency of RhB. The reaction mechanism was proposed and the results demonstrate that the role of direct photolysis on RhB dye degradation can be neglected. Meanwhile, the Langmuir-Hinshelwood kinetic model describes the photodecay date of RhB in consistent with a first order powder law and thus photocatalytic oxidation reaction followed a pseudo-first-order kinetics.

Migration of a phenolic antioxidant from aluminium oxide-poly(ethylene-co-butyl acrylate) nanocomposites in aqueous media

The migration of a phenolic antioxidant (Irganox 1010) from nanocomposites based on aluminium oxide (2–12 wt.%; uncoated or coated with aminopropyltriethoxysilane or octyltriethoxysilane) and poly(ethylene-co-butyl acrylate) (EBA) with 13 wt.% butyl acrylate nanocomposites in aqueous media (liquid water or air with 100%RH) at 90 °C was studied. The concentration of effective antioxidant in the composites was assessed by the oxidation induction time (OIT) measured by DSC. The flat OIT-profiles through the materials showed that the migration was controlled by the boundary conditions. The boundary antioxidant loss rates to the different media were (in relative units): 1 (dry air; data reported earlier), 1.5–3 (humid air) and 4–10 (liquid water). OIT-profiles for two-layer sandwich samples (a pristine EBA layer and a nanocomposite layer containing 0.2 wt.% Irganox 1010) showed that the antioxidant diffusivity was lowest in the composites containing uncoated nanoparticles (which had the highest surface concentration of hydroxyl groups of all the studied nanoparticles). The presence of water in the composites had only a small effect on the diffusivity; it was 10–50% greater than in the dry systems.

Highly‐Tunable Nickel Cobalt Oxide as a Low‐Temperature P‐Type Contact in Organic Photovoltaic Devices

AbstractWe report on the investigation of nickel cobalt oxide (NixCo3−xO4) thin films grown by pulsed laser deposition as hole‐transport interlayers (HTL) in organic photovoltaic (OPV) devices. Films of 7 nm thickness were grown under various oxygen deposition pressures (pO2) in the range of 2–200 mTorr. We explore both bulk and surface properties of these thin films. The workfunction (ϕ) for each of the films was statistically similar (∼4.7 eV), regardless of pO2. There was not a strong dependence of the power conversion efficiency (η) on the conductivities of the HTLs varying between 0.009 ‐ 10 S/cm. The observed differences in OPV efficiencies (ranging from 1.16 to 2.46%) were correlated to the near surface chemical composition of the NixCo3−xO4 HTL, as observed by differences in the relative surface hydroxyl concentration. The critical role of the near‐surface composition of the HTL at the HTL/organic interface was further explored by modifying the hydroxyl concentration using an oxygen plasma treatment. This treatment mitigated the impact of surface hydroxyl coverage, demonstrating either identical or increased values for ϕ and η, regardless of initial pO2 in the creation of the NixCo3−xO4 HTL. To further explore this we also employed a phosphonic acid surface modification agent on the HTL, increasing ϕ to 5.2 eV producing the best η value of 3.4%, equivalent to the PEDOT:PSS control devices. These results indicate that nickel cobalt oxide is a promising p‐type oxide for carrier‐selective interlayers in organic solar cells; however, for this to be fully realized the specific surface chemistry at the oxide/polymer interface must be controlled to increase ϕ and optimize device performance.