scispace - formally typeset
Search or ask a question

Showing papers in "ACS energy letters in 2016"


Journal ArticleDOI
TL;DR: In this article, a computational screening study of 2D layered transition metal carbides, MXenes, was performed for the hydrogen evolution reaction (HER) and the results showed that the basal planes of Mo2CTx are catalytically active toward the HER, unlike in the case of widely studied MoS2.
Abstract: The hydrogen evolution reaction (HER) is an important energy conversion process that underpins many clean energy technologies including water splitting. Herein, we report for the first time the application of two-dimensional (2D) layered transition metal carbides, MXenes, as electrocatalysts for the HER. Our computational screening study of 2D layered M2XTx (M = metal; X = (C, N); and Tx = surface functional groups) predicts Mo2CTx to be an active catalyst candidate for the HER. We synthesized both Mo2CTx and Ti2CTx MXenes, and in agreement with our theoretical predictions, Mo2CTx was found to exhibit far higher HER activity than Ti2CTx. Theory suggests that the basal planes of Mo2CTx are catalytically active toward the HER, unlike in the case of widely studied MoS2, in which only the edge sites of the 2H phase are active. This work paves the way for the development of novel 2D layered materials that can be applied in a multitude of other clean energy reactions for a sustainable energy future.

985 citations


Journal ArticleDOI
TL;DR: In this paper, the halide double perovskites have been proposed as a solution-processable technology to outperform multicrystalline and thin-film silicon for photovoltaics.
Abstract: Since the first reports of solar cells with power conversion efficiencies around 10% in 2012, the science and technology of perovskite photovoltaics has been progressing at an unprecedented rate. The current certified record efficiency of 22.1% makes perovskites the first solution-processable technology to outperform multicrystalline and thin-film silicon. For this technology to be deployed on a large scale, the two main challenges that need to be addressed are the material stability and the toxicity of lead. In particular, while lead is allowed in photovoltaic modules, it would be desirable to find alternatives which retain the unique optoelectronic properties of lead halide perovskites. Here we offer our perspective on the most exciting developments in the materials science of new halide perovskites, with an emphasis on alternatives to lead. After surveying recent developments of new perovskites and perovskite-related materials, we highlight the potential of halide double perovskites. This new family of...

783 citations


Journal ArticleDOI
TL;DR: In this paper, the optical and electrical properties of FAPbX3 (where X = Br − and I = I −) single crystals were investigated, and it was shown that the single crystals exhibited a 5-fold longer carrier lifetime and 10-fold lower dark carrier concentration than those of MAPbBr3 single crystals.
Abstract: State-of-the-art perovskite solar cells with record efficiencies were achieved by replacing methylammonium (MA) with formamidinium (FA) in perovskite polycrystalline films. However, these films suffer from severe structural disorder and high density of traps; thus, the intrinsic properties of FA-based perovskites remain obscured. Here we report the detailed optical and electrical properties of FAPbX3 (where X = Br– and I–) single crystals. FAPbX3 crystals exhibited markedly enhanced transport compared not just to FAPbX3 polycrystalline films but also, surprisingly, to MAPbX3 single crystals. Particularly, FAPbBr3 crystals displayed a 5-fold longer carrier lifetime and 10-fold lower dark carrier concentration than those of MAPbBr3 single crystals. We report long carrier diffusion lengths—much longer than previously thought—of 6.6 μm for FAPbI3 and 19.0 μm for FAPbBr3 crystals, the latter being one of the longest reported values in perovskite materials. These findings are of great importance for future inte...

665 citations


Journal ArticleDOI
TL;DR: In this paper, the authors discuss the thermodynamic origin and consequences of light-induced phase segregation observed in mixed-halide perovskites and propose that modifying the composition and lattice structure, increasing compositional uniformity, and reducing defect concentrations could significantly improve stability.
Abstract: In the few short years since the inception of single-junction perovskite solar cells, their efficiencies have skyrocketed. Perovskite absorbers have at least as much to offer tandem solar cells as they do for single-junction cells due in large part to their tunable band gaps. However, modifying the perovskite band structure via halide substitution, the method that has been most effective at tuning band gaps, leads to instabilities in the material for some compositions. Here, we discuss the thermodynamic origin and consequences of light-induced phase segregation observed in mixed-halide perovskites. We propose that, as the phase segregation is rooted in halide migration and possibly affected by lattice strain, modifying the perovskite composition and lattice structure, increasing compositional uniformity, and reducing defect concentrations could significantly improve stability.

503 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present experimental evidence that the enabling material property is present in the halide-lead perovskite, CH3NH3PbI3 (MAPbI), consistent with theoretical predictions.
Abstract: Photovoltaic applications of perovskite semiconductor material systems have generated considerable interest in part because of predictions that primary defect energy levels reside outside the bandgap. We present experimental evidence that this enabling material property is present in the halide-lead perovskite, CH3NH3PbI3 (MAPbI3), consistent with theoretical predictions. By performing X-ray photoemission spectroscopy, we induce and track dynamic chemical and electronic transformations in the perovskite. These data show compositional changes that begin immediately with exposure to X-ray irradiation, whereas the predominant electronic structure of the thin film on compact TiO2 appears tolerant to the formation of compensating defect pairs of VI and VMA and for a large range of I/Pb ratios. Changing film composition is correlated with a shift of the valence-band maximum only as the halide–lead ratio drops below 2.5. This delay is attributed to the invariance of MAPbI3 electronic structure to distributed def...

482 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of a series of postdeposition ligand treatments on the photoluminescence (PL) of polycrystalline methylammonium lead triiodide perovskite thin films were studied.
Abstract: We study the effects of a series of post-deposition ligand treatments on the photoluminescence (PL) of polycrystalline methylammonium lead triiodide perovskite thin films. We show that a variety of Lewis bases can improve the bulk PL quantum efficiency (PLQE) and extend the average PL lifetime, ⟨τ⟩, with large enhancements concentrated at grain boundaries. Notably, we demonstrate thin-film PLQE as high as 35 ± 1% and ⟨τ⟩ as long as 8.82 ± 0.03 μs at solar equivalent carrier densities using tri-n-octylphosphine oxide-treated films. Using glow discharge optical emission spectroscopy and nuclear magnetic resonance spectroscopy, we show that the ligands are incorporated primarily at the film surface and are acting as electron donors. These results indicate it is possible to obtain thin-film PL lifetime and PLQE values that are comparable to those from single crystals by control over surface chemistry.

447 citations


Journal ArticleDOI
TL;DR: In this article, a simple low-temperature solution-processed synthesis of pure Cs4PbBr6 with remarkable emission properties was reported, where the authors found that the pure material exhibits a 45% photoluminescence quantum yield (PLQY), in contrast to its three-dimensional counterpart, which exhibits more than 2 orders of magnitude lower PLQY.
Abstract: So-called zero-dimensional perovskites, such as Cs4PbBr6, promise outstanding emissive properties. However, Cs4PbBr6 is mostly prepared by melting of precursors that usually leads to a coformation of undesired phases. Here, we report a simple low-temperature solution-processed synthesis of pure Cs4PbBr6 with remarkable emission properties. We found that pure Cs4PbBr6 in solid form exhibits a 45% photoluminescence quantum yield (PLQY), in contrast to its three-dimensional counterpart, CsPbBr3, which exhibits more than 2 orders of magnitude lower PLQY. Such a PLQY of Cs4PbBr6 is significantly higher than that of other solid forms of lower-dimensional metal halide perovskite derivatives and perovskite nanocrystals. We attribute this dramatic increase in PL to the high exciton binding energy, which we estimate to be ∼353 meV, likely induced by the unique Bergerhoff–Schmitz–Dumont-type crystal structure of Cs4PbBr6, in which metal-halide-comprised octahedra are spatially confined. Our findings bring this class...

438 citations


Journal ArticleDOI
TL;DR: In this article, the authors elucidate how halide compositions control both of these correlated parameters of CsPbX3 nanocrystals and show that the valence band maximum (VBM) shifts significantly to higher energies by 0.80 eV, from X = Cl to Br to I, whereas the shift in the conduction band minimum (CBM) is small (0.19 eV) but systematic.
Abstract: Colloidal CsPbX3 (X = Cl, Br, and I) nanocrystals have recently emerged as preferred materials for light-emitting diodes, along with opportunities for photovoltaic applications. Such applications rely on the nature of valence and conduction band edges and optical transitions across these edges. Here we elucidate how halide compositions control both of these correlated parameters of CsPbX3 nanocrystals. Cyclic voltammetry shows that the valence band maximum (VBM) shifts significantly to higher energies by 0.80 eV, from X = Cl to Br to I, whereas the shift in the conduction band minimum (CBM) is small (0.19 eV) but systematic. Halides contribute more to the VBM, but their contribution to the CBM is also not negligible. Excitonic transition probabilities for both absorption and emission of visible light decrease probably because of the increasing dielectric constant from X = Cl to Br to I. These band edge properties will help design suitable interfaces in both devices and heterostructured nanocrystals.

393 citations


Journal ArticleDOI
TL;DR: It is demonstrated that the combination of Ag(I) and Bi(III) leads to the wide indirect band gaps with large carrier effective masses owing to a mismatch in angular momentum of the frontier atomic orbitals, which can be overcome by replacing Ag with In or Tl; however, the resulting compounds are predicted to be unstable thermodynamically.
Abstract: The methylammonium lead halides have become champion photoactive semiconductors for solar cell applications; however, issues still remain with respect to chemical instability and potential toxicity. Recently, the Cs2AgBiX6 (X = Cl, Br) double perovskite family has been synthesized and investigated as stable nontoxic replacements. We probe the chemical bonding, physical properties, and cation anti-site disorder of Cs2AgBiX6 and related compounds from first-principles. We demonstrate that the combination of Ag(I) and Bi(III) leads to the wide indirect band gaps with large carrier effective masses owing to a mismatch in angular momentum of the frontier atomic orbitals. The spectroscopically limited photovoltaic conversion efficiency is less than 10% for X = Cl or Br. This limitation can be overcome by replacing Ag with In or Tl; however, the resulting compounds are predicted to be unstable thermodynamically. The search for nontoxic bismuth perovskites must expand beyond the Cs2AgBiX6 motif.

370 citations


Journal ArticleDOI
TL;DR: In this article, a 1 cm2 near-infrared transparent perovskite solar cell with 14.5% steady-state efficiency was presented, as compared to 16.4% on 0.25 cm2.
Abstract: Combining market-proven silicon solar cell technology with an efficient wide band gap top cell into a tandem device is an attractive approach to reduce the cost of photovoltaic systems. For this, perovskite solar cells are promising high-efficiency top cell candidates, but their typical device size (<0.2 cm2), is still far from standard industrial sizes. We present a 1 cm2 near-infrared transparent perovskite solar cell with 14.5% steady-state efficiency, as compared to 16.4% on 0.25 cm2. By mechanically stacking these cells with silicon heterojunction cells, we experimentally demonstrate a 4-terminal tandem measurement with a steady-state efficiency of 25.2%, with a 0.25 cm2 top cell. The developed top cell processing methods enable the fabrication of a 20.5% efficient and 1.43 cm2 large monolithic perovskite/silicon heterojunction tandem solar cell, featuring a rear-side textured bottom cell to increase its near-infrared spectral response. Finally, we compare both tandem configurations to identify effic...

329 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the intrinsic instability mechanism of the α-phase at ambient temperature and demonstrated the existence of an anisotropic strained lattice in the (111) plane that drives phase transformation into the δ-phase.
Abstract: Though formamidinium lead triiodide (FAPbI3) possesses a suitable band gap and good thermal stability, the phase transition from the pure black perovskite phase (α-phase) to the undesirable yellow nonperovskite polymorph (δ-phase) at room temperature, especially under humid air, hinders its practical application. Here, we investigate the intrinsic instability mechanism of the α-phase at ambient temperature and demonstrate the existence of an anisotropic strained lattice in the (111) plane that drives phase transformation into the δ-phase. Methylammonium bromide (MABr) alloying (or FAPbI3-MABr) was found to cause lattice contraction, thereby balancing the lattice strain. This led to dramatic improvement in the stability of α-FAPbI3. Solar cells fabricated using FAPbI3-MABr demonstrated significantly enhanced stability under the humid air.

Journal ArticleDOI
TL;DR: In this article, a type of NiCoFe layered triple hydroxides (LTHs) supported on carbon fiber cloth (CFC) was used as high performance electrocatalysts for overall water splitting in alkaline media.
Abstract: We report a type of NiCoFe layered triple hydroxides (LTHs) supported on carbon fiber cloth (CFC) (NiCoFe LTHs/CFC) as high-performance electrocatalysts for overall water splitting in alkaline media. The NiCoFe LTHs/CFC as an oxygen evolution reaction (OER) electrocatalyst shows excellent catalytic activity and durability, such as low overpotential of ∼239 mV at 10 mA cm–2, small Tafel slope of ∼32 mV dec–1 and conservation rate of catalytic activity (∼99%) after 12 h of continuous electrolysis at 20 mA cm–2. As a hydrogen evolution reaction (HER) electrocatalyst, NiCoFe LTHs/CFC also shows low onset potential, small Tafel slope, and superior durability. The NiCoFe LTHs/CFC-based overall water splitting exhibits a low onset potential (∼1.51 V), a low splitting potential (∼1.55 V) at 10 mA cm–2, and excellent durability, and the performance is comparable to that of IrO2/Pt-based overall water splitting. This work will open a new avenue toward the development of high-performance and inexpensive layered trip...

Journal ArticleDOI
TL;DR: In this article, the phase separation of halide ion movement in mixed halide films is tracked through excited-state behavior using emission and transient absorption spectroscopy tools, and the time scale with which such separation occurs under laser irradiation (405 nm, 25 mW/cm2 to 1.7 W/cm 2) as well as dark recovery.
Abstract: Mixed halide lead perovskites (e.g., CH3NH3PbBrxI3–x) undergo phase segregation creating iodide-rich and bromide-rich domains when subjected to visible irradiation. This intriguing aspect of halide ion movement in mixed halide films is now being tracked through excited-state behavior using emission and transient absorption spectroscopy tools. These transient experiments have allowed us to establish the time scale with which such separation occurs under laser irradiation (405 nm, 25 mW/cm2 to 1.7 W/cm2) as well as dark recovery. While the phase separation occurs with a rate constant of 0.1–0.3 s–1, the recovery occurs over a time period of several minutes to an hour. The relative photoluminescence quantum yield observed for Br-rich regions (em. max 530 nm) is nearly 2 orders of magnitude lower than that of I-rich regions (em. max 760 nm) and arises from the fact that I-rich regions serve as sinks for photogenerated charge carriers. Understanding such cascading charge transfer to localized sites could furth...

Journal ArticleDOI
TL;DR: In this paper, a nickel-based oxygen evolution catalyst derived from pulse-electrodeposited nickel sulfide was found to produce current densities of 10 mA/cm2 at the relatively low overpotential of 320 mV in alkaline electrolyte (1 M KOH).
Abstract: Oxygen evolution catalysts composed of a metal (Ni, Co, or Fe) and a pnictide or chalcogenide (P, S, or Se) counterion are a promising class of electrocatalysts for the oxygen evolution reaction (OER), an important reaction for the photoelectrochemical splitting of water. We synthesized a nickel-based oxygen evolution catalyst derived from pulse-electrodeposited nickel sulfide. This catalyst was found to produce current densities of 10 mA/cm2 at the relatively low overpotential of 320 mV in alkaline electrolyte (1 M KOH). Importantly, we found that the sulfur anion in the nickel sulfide is depleted in the active form of the electrocatalyst and that the NiS is converted into an amorphous nickel oxide in the potential range where water is oxidized to oxygen. The superior catalytic activity of this nickel sulfide is thus unrelated to the sulfur anions in the active catalyst but is instead related to the metal sulfide’s ability to act as a precursor to a highly active nickel oxide OER electrocatalyst. The nic...

Journal ArticleDOI
TL;DR: In this article, a solution-based fabrication and characterization of the lead-free perovskite-related methylammonium antimony iodide (CH3NH3)3Sb2I9 compound was presented.
Abstract: We present solution-based fabrication and characterization of the lead-free perovskite-related methylammonium antimony iodide (CH3NH3)3Sb2I9 compound. By photothermal deflection spectroscopy (PDS), we determined a peak absorption coefficient α ≈ 105 cm–1 and an optical band gap of 2.14 eV for amorphous films of (CH3NH3)3Sb2I9. Compared to the related Bi compound, the Sb-perovskite shows no exciton peak in its absorption spectrum. The photoluminescence emission (PL) is observed at 1.58 eV, and the Urbach tail energy of this amorphous compound is Eu = 62 meV, indicating a substantial amount of energetic disorder. We fabricate a planar heterojunction solar cell with a (CH3NH3)3Sb2I9 absorber layer that yields a power conversion efficiency of η ≈ 0.5%, already featuring a decent fill factor (FF) of 55% and open-circuit voltage of 890 mV but low photocurrent densities. The result of this basic study on (CH3NH3)3Sb2I9 shows that this compound is a possible starting point for further research into Sb-based lead-...

Journal ArticleDOI
TL;DR: In this article, a simple defect passivation method was exploited by post-treating CH3NH3PbI3 (MAPbI 3) film with a rationally selected diammonium iodide.
Abstract: The polycrystalline feature of solution-processed perovskite film and its ionic nature inevitably incur substantial crystallographic defects, especially at the film surface and the grain boundaries (GBs). Here, a simple defect passivation method was exploited by post-treating CH3NH3PbI3 (MAPbI3) film with a rationally selected diammonium iodide. The molecular structure of the used diammonium iodide was discovered to play a critical role in affecting the phase purity of treated MAPbI3. Both NH3I(CH2)4NH3I and NH3I(CH2)2O(CH2)2NH3I (EDBE) induce three-dimensional (3D) to two-dimensional (2D) perovskite phase transformation during the treatment while only NH3I(CH2)8NH3I (C8) successfully passivates perovskite surface and GBs without forming 2D perovskite because of the elevated activation energy arising from its unique anti–gauche isomerization. Defect passivation of MAPbI3 was clearly confirmed by scanning Kelvin probe microscopy (SKPM) and time-resolved photoluminescence (TRPL) studies, which results in th...

Journal ArticleDOI
TL;DR: In this paper, layered TiS2 was used as a promising positive electrode intercalation material, providing 115 mAh/g/1 stabilized capacity in a Mg full cell.
Abstract: Magnesium batteries are a good candidate for high energy storage systems, but the limited discovery of functional positive electrode materials beyond the seminal Chevrel phase (Mo6S8) has slowed their development. Herein, we report on layered TiS2 as a promising positive electrode intercalation material, providing 115 mAh g–1 stabilized capacity in a Mg full cell. Reversible Mg2+ intercalation into the structure is proven by elemental analysis combined with X-ray diffraction studies that elucidate the phase behavior upon cycling. The voltage profiles reveal distinct Mg2+ cation ordering, unlike the solid solution behavior exhibited by Li+. Our findings not only point to the important role of “soft” lattices to facilitate divalent solid-state cation mobility but also now provide an alternative sulfide to serve as a platform for the fundamental understanding of Mg2+ intercalation in lattices.


Journal ArticleDOI
TL;DR: In this article, a highly viscoelastic polymer was applied to the lithium metal electrode, and the morphology of the lithium deposition became significantly more uniform at a high current density of 5 mA/cm2.
Abstract: The future development of low-cost, high-performance electric vehicles depends on the success of next-generation lithium-ion batteries with higher energy density. The lithium metal negative electrode is key to applying these new battery technologies. However, the problems of lithium dendrite growth and low Coulombic efficiency have proven to be difficult challenges to overcome. Fundamentally, these two issues stem from the instability of the solid electrolyte interphase (SEI) layer, which is easily damaged by the large volumetric changes during battery cycling. In this work, we show that when a highly viscoelastic polymer was applied to the lithium metal electrode, the morphology of the lithium deposition became significantly more uniform. At a high current density of 5 mA/cm2 we obtained a flat and dense lithium metal layer, and we observed stable cycling Coulombic efficiency of ∼97% maintained for more than 180 cycles at a current density of 1 mA/cm2.

Journal ArticleDOI
TL;DR: In this article, a networked polymer electrolyte simultaneously displays tLi+ approaching unity and high ionic conductivity (σ ≈ 10−4 S cm−1 at 25 °C).
Abstract: Safety issues rising from the use of conventional liquid electrolytes in lithium-based batteries are currently limiting their application to electric vehicles and large-scale energy storage from renewable sources. Polymeric electrolytes represent a solution to this problem due to their intrinsic safety. Ideally, polymer electrolytes should display both high lithium transference number (tLi+) and ionic conductivity. Practically, strategies for increasing tLi+ often result in low ionic conductivity and vice versa. Herein, networked polymer electrolytes simultaneously displaying tLi+ approaching unity and high ionic conductivity (σ ≈ 10–4 S cm–1 at 25 °C) are presented. Lithium cells operating at room temperature demonstrate the promising prospect of these materials.

Journal ArticleDOI
TL;DR: In this paper, an all-inorganic lead-free perovskite option, cesium tin bromide (CsSnBr3), was explored for optoelectronic applications.
Abstract: Solar cells based on “halide perovskites” (HaPs) have demonstrated unprecedented high power conversion efficiencies in recent years. However, the well-known toxicity of lead (Pb), which is used in the most studied cells, may affect its widespread use. We explored an all-inorganic lead-free perovskite option, cesium tin bromide (CsSnBr3), for optoelectronic applications. CsSnBr3-based solar cells exhibited photoconversion efficiencies (PCEs) of 2.1%, with a short-circuit current (JSC) of ∼9 mA cm–2, an open circuit potential (VOC) of 0.41 V, and a fill factor (FF) of 58% under 1 sun (100 mW cm–2) illumination, which, even though meager compared to the Pb analogue-based cells, are among the best reported until now. As reported earlier, addition of tin fluoride (SnF2) was found to be beneficial for obtaining good device performance, possibly due to reduction of the background carrier density by neutralizing traps, possibly via filling of cation vacancies. The roles of SnF2 on the properties of the CsSnBr3 we...

Journal ArticleDOI
TL;DR: In this article, the formation of a functional solid electrolyte interphase (SEI) in sodium ion batteries is hampered by the higher solubility of SEI components such as sodium salts in comparison to the lithium analogues.
Abstract: It is often stated that formation of a functional solid electrolyte interphase (SEI) in sodium ion batteries is hampered by the higher solubility of SEI components such as sodium salts in comparison to the lithium analogues. In order to investigate these phenomena, SEI formation and functionality, as well as cell self-discharge, are studied for the sodium ion system with comparative experiments on the equivalent lithium ion system. By conducting a set of experiments on carbonaceous anodes, the impact of SEI dissolution is tested. The results show that the SEI layer in sodium ion cells is inferior to that in lithium ion counterparts with regards to self-discharge; sodium cells show a loss in capacity at a dramatic rate as compared to the lithium counterparts when they are stored at sodiated and lithiated states, respectively, for a long time with no external applied current or potential. Also, synchrotron-based hard X-ray photoelectron spectroscopy measurements indicate that the major factor leading to inc...

Journal ArticleDOI
TL;DR: In this article, the stability of methylammonium lead iodide perovskite photovoltaic devices with various hole-collecting anode configurations was investigated.
Abstract: We investigated and characterized the stability of the power output from methylammonium lead iodide perovskite photovoltaic devices produced with various hole-collecting anode configurations consisting of Au, Ag, MoOx/Au, MoOx/Ag, and MoOx/Al. The unencapsulated devices were operated under constant illumination and constant load conditions in laboratory ambient with periodic current–voltage testing. Although the initial efficiencies of devices were comparable across these configurations, the stability of these devices varied significantly due to subtle differences in the electrode structure. Specifically, we found that devices with MoOx/Al electrodes are more stable than devices with more conventional, and more costly, Au and Ag electrodes. We demonstrate that a thin MoOx layer inhibits decomposition of the perovskite films under illumination in ambient laboratory conditions and greater improvements in device stability are achieved specifically with MoOx/Al electrodes. We investigated the role of the MoOx...

Journal ArticleDOI
TL;DR: In this paper, needle-shaped narrow hexagonal phase 1D nanostructures of dicobalt phosphide (Co2P) are reported as efficient electrocatalysts for the oxygen evolution reaction (OER).
Abstract: Needle-shaped narrow hexagonal phase 1D nanostructures of dicobalt phosphide (Co2P) are reported as efficient electrocatalysts for the oxygen evolution reaction (OER). Without other metal incorporation, which was typically followed for enhancing the OER activity, the electrochemical performance was observed to be superior in comparison to all reported cobalt-based nanostructured metal phosphides. For anodic metamorphosis, these nanostructures, like all other metal phosphides, undergo surface oxidation but remain more active and superior to pure cobalt oxides as well as surface-oxidized different shaped monocobalt phosphides. Moreover, the synthesis was also followed by adopting a moderate synthetic protocol where PH3 gas was used as a phosphorus source and also scaled up to the gram level. In addition, the hydrogen evolution reaction (HER) performance of these phosphides was further studied, and the performance was observed to be comparable to that in the best reports.

Journal ArticleDOI
Abstract: Electrocatalytic biomass valorization with renewable energy input represents a promising way to produce sustainable and nonfossil-based carbon products. Even more desirable is that the oxidative biomass upgrading can be integrated with H2 production in a single electrolyzer. Herein, we report that electrodeposited Co–P can act as competent electrocatalysts for 5-hydroxymethylfurfural (HMF) oxidation to 2,5-furandicarboxylic acid (FDCA) at the anode and H2 production at the cathode simultaneously in alkaline media. When serving as a catalyst precursor on the anode, Co–P was able to achieve a current density of 20 mA/cm2 for HMF oxidation in 1.0 M KOH with 50 mM HMF at 1.38 V vs RHE, prior to the takeoff of the competing reaction, O2 evolution. Long-term chronoamperometry demonstrated a nearly 100% conversation of HMF and a ∼90% yield of FDCA. When HMF oxidation and H2 evolution were integrated in one electrolyzer with a Co–P/Co–P catalyst couple, the potential required to achieve a current density of 20 mA...

Journal ArticleDOI
TL;DR: In this paper, the authors measured phonon dispersions in CH3NH3PbI3 and found direct evidence for another form of disorder in single crystals: large-amplitude anharmonic zone edge rotational instabilities of the PbI6 octahedra that persist to room temperature and above.
Abstract: Lead halide perovskites such as methylammonium lead triiodide (CH3NH3PbI3) have outstanding optical and electronic properties for photovoltaic applications, yet a full understanding of how this solution-processable material works so well is currently missing. Previous research has revealed that CH3NH3PbI3 possesses multiple forms of static disorder regardless of preparation method, which is surprising in light of its excellent performance. Using high energy resolution inelastic X-ray (HERIX) scattering, we measure phonon dispersions in CH3NH3PbI3 and find direct evidence for another form of disorder in single crystals: large-amplitude anharmonic zone edge rotational instabilities of the PbI6 octahedra that persist to room temperature and above, left over from structural phase transitions that take place tens to hundreds of degrees below. Phonon calculations show that the orientations of the methylammonium (CH3NH3+) couple strongly and cooperatively to these modes. The result is a noncentrosymmetric, insta...

Journal ArticleDOI
TL;DR: In this article, an inorganic halide perovskite solar cell using a spray-assisted solution-processed CsPbIBr2 film is demonstrated, overcoming the solubility problem of bromide ion in the precursor solution that would otherwise occur in a single-step solution process.
Abstract: In this work, an inorganic halide perovskite solar cell using a spray-assisted solution-processed CsPbIBr2 film is demonstrated. The process allows sequential solution processing of the CsPbIBr2 film, overcoming the solubility problem of the bromide ion in the precursor solution that would otherwise occur in a single-step solution process. The spraying of CsI in air is demonstrated to be successful, and the annealing of the CsPbIBr2 film in air is also successful in producing a CsPbIBr2 film with an optical band gap of 2.05 eV and is thermally stable at 300 °C. The effects of the substrate temperature during spraying and the annealing temperature on film quality and device performance are studied. The substrate temperature during spraying is found to be the most critical parameter. The best-performing device fabricated using these conditions achieves a stabilized conversion efficiency of 6.3% with negligible hysteresis. Cesium metal halide perovskites remain viable alternatives to organic metal halide per...

Journal ArticleDOI
TL;DR: In this paper, the electrolysis of CO2 to syngas (CO + H2) using nonprecious metal electrocatalysts was studied in bipolar membrane-based electrochemical cells.
Abstract: The electrolysis of CO2 to syngas (CO + H2) using nonprecious metal electrocatalysts was studied in bipolar membrane-based electrochemical cells. Electrolysis was carried out using aqueous bicarbonate and humidified gaseous CO2 on the cathode side of the cell, with Ag or Bi/ionic liquid cathode electrocatalysts. In both cases, stable currents were observed over a period of hours with an aqueous alkaline electrolyte and NiFeOx electrocatalyst on the anode side of the cell. In contrast, the performance of the cells degraded rapidly when conventional anion- and cation-exchange membranes were used in place of the bipolar membrane. In agreement with earlier reports, the Faradaic efficiency for CO2 reduction to CO was high at low overpotential. In the liquid-phase bipolar membrane cell, the Faradaic efficiency was stable at about 50% at 30 mA/cm2 current density. In the gas-phase cell, current densities up to 200 mA/cm2 could be obtained, albeit at lower Faradaic efficiency for CO production. At low overpotenti...

Journal ArticleDOI
TL;DR: In this article, a comprehensive study of perovskite optoelectronic device degradation was performed using in situ X-ray diffraction measurements, and it was shown that redox reactions are fundamental to the degradation process for CH3NH3PbI3, CsPbBr3, and CsPsPbBI3 with Ag, Al, Yb, or Cr contacts.
Abstract: We report a comprehensive study of the chemistry of perovskite optoelectronic device degradation and show that redox reactions are fundamental to the degradation process for CH3NH3PbI3, CsPbI3, and CsPbBr3 perovskites with Ag, Al, Yb, or Cr contacts. Using in situ X-ray diffraction measurements, we study the chemistry of CH3NH3PbI3 perovskite devices equipped with Al electrodes; we find that Al0 rapidly reduces Pb2+ to Pb0, converting CH3NH3PbI3 first to (CH3NH3)4PbI6·2H2O and then to CH3NH3I. In situ scanning electron microscopy measurements show that moisture enables continued reaction of the Al and perovskite layers by facilitating ion diffusion, before serving as a decomposition reagent for the perovskite film. Redox reactions follow what is expected based on standard electrochemical potentials for Al, Cr, and Yb; for Ag, the redox chemistry is enabled by the presence of iodide. We emphasize that critical chemical reactions can stem from intrinsic interfacial interactions between the layers in a devic...

Journal ArticleDOI
TL;DR: In this paper, the effect of size, shape, and halide composition on the electronic structure of PNCs was analyzed with density functional theory, and it was shown that the PNC crystalline core exhibits an orthorhombic structure.
Abstract: Colloidal cesium lead halide perovskite nanocrystals (CsPbX3 PNCs, X = Cl, Br, I) exhibit important optoelectronic properties that make them amenable for a plethora of applications. However, the origin of these properties, even for as-synthesized and unpurified PNCs, is largely unknown. Electronic structure calculations are therefore essential to understand with atomistic detail the properties of these nanomaterials; however, finding a model for PNCs that resembles the experiments is a challenging task. Essentially, the main problem is how to correctly terminate a PNC surface that is comprised of a large fraction of the nanocrystal atoms and of ligands employed in the synthesis. Here, we construct nominally trap-free models for PNCs taking into account experimental conditions. With density functional theory we analyze the effect of size, shape, and halide composition on the electronic structure of PNCs. We confirm that the PNC crystalline core exhibits an orthorhombic structure, and we demonstrate that PN...