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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Cobalt(II) Phthalocyanine Substituents Tune the Electrocatalytic CO 2 Conversion to Methanol

Cobalt phthalocyanine (Co(II)Pc) and its derivatives are promising molecular electrocatalysts for the electrochemical reduction of CO 2 to CO and methanol (CH 3 OH). Despite increasing interest, a detailed mechanistic understanding of how ligand substituents influence catalytic activity, selectivity, and efficiency remains limited. In this study, we employ density functional theory (DFT) to systematically investigate the influence of electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) on the electronic structure and redox properties of the Co(II)Pc electrocatalyst, and to elucidate CO 2 RR mechanistic pathways. Our results reveal that EWGs cause a positive shift in the reduction potentials, favor CO 2 binding over protonation of the Co metal center and promote downstream methanol formation at mild potentials. EDGs show opposite trends including favorable protonation steps, promoting a negative shift in the reduction potential, and facilitating the hydrogen evolution reaction (HER), which competes with the desired CO 2 RR pathway. Notably, CO dissociation is thermodynamically and kinetically unfavorable across all systems, positioning the redox potential versus CO dissociation energy as a key factor for methanol selectivity. Furthermore, these insights provide a predictive framework for rational catalyst design and underscore the critical role of electronic tuning in advancing molecular electrocatalysts for sustainable CO 2 conversion.

Alcohols↗
DOE OSTI2026

From Serendipity to Exploration: Synthesis and Properties of PtSiSb

PtSiSb is a compound with covalent Si–Sb bonds, which are relatively rare instances in solid-state materials. The original report on PtSiSb indicates synthetic challenges for the isolation of single-phase samples, as well as potential discrepancies in the predicted electronic structure and experimental transport properties. In this work, we considered PtSiSb as a case study with the objective of demonstrating the importance of synthesis as a bridge between theoretical predictions and experimental properties. Using guidance from in situ powder X-ray diffraction, the synthesis of single-phase polycrystalline samples was developed, allowing further experimental characterization of transport and catalytic properties. Thermal conductivity and heat capacity demonstrated anomalous behavior, indicating an unconventional phonon scattering mechanism in PtSiSb. Charge transport measurements indicated semimetallic behavior. Hydrogen evolution reaction (HER) tests in acidic electrolyte revealed that the PtSiSb cathode needs an overpotential η 10 = 120 mV to achieve a current density j = −10 mA/cm 2 . This is lower activity than elemental Pt but comparable to known and active transition-metal phosphide HER catalysts, such as CoP, with η 10 = 93 mV when measured at identical conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

A Theoretical Benchmark of the Geometric and Optical Properties for 3d Transition Metal Nanoclusters via Density Functional Theory

Understanding structure–property relationships in atomically precise metal nanoclusters is vital in finding selective and tunable catalysts. Here, in this study, density functional theory (DFT) was used to benchmark seven exchange correlation functionals at different basis sets for 17 atomically precise nanoclusters against experimentally determined geometries, band gaps, and optical gaps. The set contains both monometallic and bimetallic clusters that possess at least two types of 3d transition metals (specifically, Cu, Ni, Fe, or Co). The benchmark highlights that PBE0 is a good functional to use regardless of the basis set, and Minnesota functionals do well with respect to specific metals. Further, while long-range corrected functionals overestimate band and optical gaps, they model absorption features better than the other considered functionals. The study additionally looks at the photoinduced hydrogen evolution reaction (HER) and the CO 2 reduction mechanism on nanoclusters reported from the literature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Locally Engineering and Interrogating the Photoelectrochemical Behavior of Defects in Transition Metal Dichalcogenides

Transition metal dichalcogenides (TMDs) are attractive materials for a variety of applications in solar energy conversion and electrocatalysis, due to their favorable optical and electrical properties and their unique two-dimensional structures which facilitate the fabrication of wide-area, ultrathin layers. Unfortunately, the basal planes which make up the majority of these materials are relatively inert, and thus a great deal of effort has been directed to engineering favorable, catalytically active defects into these materials. In this paper, we demonstrate how probe-based electrochemical techniques can be employed as multifunctional tools for locally modifying TMD materials and probing the electrochemical behavior of the resulting defects. Scanning Electrochemical Cell Microscopy (SECCM) was employed to locally anodize exfoliated p-type WSe 2 nanosheets, creating hole-like defects within individual basal planes in a highly controllable fashion. Photoelectrochemical SECCM imaging was then employed to characterize the chemical behavior of these engineered defects, revealing significantly enhanced activity toward the Hydrogen Evolution Reaction (HER). Atomic force microscopy studies are presented which suggest these enhancements result from an increased density of monolayer-high step features within the anodized defects. Analysis of the SECCM data in the context of finite element simulations revealed that these enhancements increased with increasing anodization time, with local kinetic rates over 2 orders of magnitude higher than unaltered basal planes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Electronic Structure of Molecular Cobalt Catalysts for H 2 Production Revealed by Multifrequency EPR

Improving the design of hydrogen evolution reaction (HER) catalysts requires a detailed understanding of the catalyst's structure and environment. Here wwe have used multifrequency electron paramagnetic resonance (EPR) spectroscopy (X-band, Q-band, and D-band) in combination with density functional theory (DFT) modeling to elucidate the electronic structure of three Co(II) molecular catalysts for H 2 evolution to determine correlations of electronic structure parameters with catalytic activity and stability. The Co(II) coordination complexes investigated here are representative of two types of H 2 -evolving molecular catalysts: cobaloximes, formed from cobalt coordination to two glyoxime ligands, and cobalt poly(pyridyl) complexes, which commonly have either four or five pyridyl ligands coordinating a single Co(II) ion. These Co(II) complexes were studied in a variety of solvents with a range of polarities and stoichiometric amounts of potential ligands to the cobalt ion to assess the strength and nature of ligand- cobalt interactions. Using magnetic resonance parameters obtained by EPR spectroscopy as reference data, we reconstructed the electronic structure of the Co(II) complexes with the help of DFT modeling. For all three catalysts, we uncovered a linear correlation between the Co(II) A z value and the g x value that is dependent on the strength of the axial ligands. The correlations that we have established between the electronic structure and metal coordination environment provide insight into the structural and electronic factors underpinning the observed trends in HER catalysis activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Probing Electrolyte Influence on CO 2 Reduction in Aprotic Solvents

Selective CO 2 capture and electrochemical conversion are important tools in the fight against climate change. Industrially, CO 2 is captured using a variety of aprotic solvents due to their high CO 2 solubility. However, most research efforts on electrochemical CO 2 conversion use aqueous media and are plagued by competing hydrogen evolution reaction (HER) from water breakdown. Fortunately, aprotic solvents can circumvent HER, making it important to develop strategies that enable integrated CO 2 capture and conversion. However, the influence of ion solvation and solvent selection within nonaqueous electrolytes for efficient and selective CO 2 reduction is unclear. In this work, we show that the bulk solvation behavior within the nonaqueous electrolyte can control the CO2 reduction reaction and product distribution occurring at the catalyst-electrolyte interface. We study different tetrabutylammonium (TBA) salts in two electrolyte systems with glyme ethers (e.g., 1,2 dimethoxyethane or DME) and dimethyl sulfoxide (DMSO) as a low and high dielectric constant medium, respectively. Using spectroscopic tools, we quantify the fraction of ion pairs that forms within the electrolyte. Also, we show how ion pair formation is prevalent in DME and is dependent on the anion type. More importantly, we show that as ion pair formation decreases within the electrolyte, CO 2 current densities increase, and a higher CO Faradaic efficiency is observed at low overpotentials. Meanwhile, in an electrolyte medium where the ion pair fraction does not change with the anion type (such as in DMSO), a smaller influence of solvation is observed on CO 2 current densities and product distribution. By directly coupling bulk solvation to interfacial reactions and product distribution, we showcase the importance and utility of controlling the reaction microenvironment in tuning the electrocatalytic reaction pathways. Insights gained from this work will enable novel electrolyte designs for efficient and selective CO 2 conversion to desired fuels and chemicals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Metal–Organic Framework as a Dual Support for Organic Photosensitizers and Single-Atom Catalysts

Metal–organic framework (MOF)-supported single-atom catalysts (SACs) possess integrated unique capabilities of both MOF and SACs, which represent a promising class of catalysts for photocatalytic applications. Herein, we report the incorporation of nickel (Ni) SACs onto its zirconium node and the functionalization of the organic linker of the zirconium MOF with perylene tetracarboxylic dianhydride (PDA), resulting in the formation of a hybrid MOF (denoted as Ni-PiU) with significantly enhanced light absorption ability in the visible region. Using the combination of time-resolved emission and X-ray absorption spectroscopy, we show that efficient charge separation occurs by electron transfer from incorporated PDA to Ni SACs with super slow charge recombination dynamics. As a result of these important photophysical properties, Ni-PiU MOF exhibits excellent photocatalytic activity and durability for the hydrogen evolution reaction. Finally, this work demonstrates the unique ability of MOFs as a dual platform to incorporate both SACs and a light absorption unit into their framework, providing a promising strategy for rational design of next-generation photocatalytic materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Cations Enhance Hydride Transfer to Noncatalytic Metals in Concentrated Alkaline Electrolytes

Alkali metal cations are known to influence the kinetics of the hydrogen evolution reaction (HER), acting as either promoters or inhibitors to the rate-determining step depending on the metal surface, local pH, and cation concentration. Despite the importance of concentrated electrolytes for commercial electrochemical cells, the impact of cations on the HER in concentrated alkaline environments (>1 M) and in mixed cation systems remains poorly understood. Here, this study quantifies the HER kinetics at polycrystalline metal surfaces (Pt, Au, Cu, and Fe) and the equilibrium solvation environment in pure and mixed alkali metal hydroxide electrolytes at concentrations up to 3.0 M. Kinetic analyses of Au, Cu, and Fe revealed a positive cation-concentration-effect that was primarily driven by changes to the charge transfer coefficient. Multinuclear NMR spectroscopy examined the solvation of H 2 O/OH – species and the alkali cations as a function of (mixed) alkali cation concentration(s), and demonstrated rapid exchange between solvent, hydroxide, and solvated cations. Together, these findings support models where HER kinetics on noncatalytic metal surfaces in strongly alkaline conditions are primarily governed by the average polarization and polarizability of the metal/solution interface and that increasing cation activity continues to increase the transfer coefficient at metal-hydroxide concentrations up to 3.0 M. Electrolytes and additives which can outcompete weakly hydrated cations and disrupt the interfacial water structure are expected to suppress parasitic HER at electrodes for energy storage and electroplating.

Cations↗
DOE OSTI2022

Atomically Dispersed CuN x Sites from Thermal Activation of Boron Imidazolate Cages for Electrocatalytic Methane Generation

Atomically dispersed metal sites (ADMSs) have been recognized as promising candidates for electrochemical conversion. Among a diverse range of molecular precursors for ADMS synthesis, framework materials are particularly interesting due to their high degree of tunability and control over the primary coordination sphere of the metal ions. In this work, we demonstrate that a copper boron imidazolate cage, BIF-29(Cu), is a convenient precursor for a competent catalyst with isolated Cu sites coordinated by N donors for carbon dioxide electroreduction (CO 2 RR). Although BIF-29(Cu) exhibited moderate methane selectivity over hydrogen evolution reaction (HER), the methane selectivity is significantly enhanced by 2 times (55% CH 4 at –1.25 V vs RHE) after mild thermal activation. Extensive characterization methods indicate the transformation of crystalline BIF-29(Cu) into an amorphous carbonaceous material comprising isolated CuN x sites. Moreover, in situ X-ray absorbance spectroscopy indicates stable CuN x sites that are reduced during CO 2 RR. This work encourages the discovery of single-site electrocatalytic systems through a rational selection of molecular precursor and calcination parameters for promoting product selectivity.

10 SYNTHETIC FUELS↗
DOE OSTI2025

Anolyte Buffering and CO Coverage Effects in the Electrochemical Reduction of CO at Cu Electrocatalysts

Electrolytic CO reduction was investigated at copper electrocatalysts in zero-gap membrane electrode assemblies as a function of buffering agents and cofeeding with CO 2 or Ar. Results show an acetate Faradaic efficiency (FE) of 90% at 300 mA cm −2 using pure CO feeds and phosphate-buffered anolyte near pH 8. When using CO feeds with more alkaline anolytes, the hydrogen evolution reaction becomes the dominant reduction reaction, independent of the buffer. Product distributions of cofeeding experiments with CO and CO 2 show that increasing CO 2 cofeeding results in increased selectivity toward ethylene (42% FE) in near-neutral KHCO 3 anolytes or ethanol (40% FE) in alkaline KOH anolytes. Evaluation of several commercial anion exchange membranes shows similar selectivity trends, suggesting product selectivity is dominated by the local pH and surface coverage of CO. Based on these results, we propose pH buffering and CO coverage behaviors that facilitate high selectivities to acetate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Tuning the Charge Transport Property and Photocatalytic Activity of Anthracene-Based 1D π–d Conjugated Coordination Polymers by Interlayer Stacking

One-dimensional (1D) π–d-conjugated coordination polymers (CCPs) with charge delocalization have attracted significant attention due to their potential application in energy conversion and storage. However, the fundamental understanding of the correlation of their structural parameters with photophysical and photocatalytic properties remains underexplored. Herein, we report three novel Cu-node anthracene-based 1D π–d CCPs with systematic variation of steric groups (Ph > Me > H) at the 9 and 10 position of anthracene (denoted as An Ph , An Me , and An H ), which is aimed at altering the stacking of the polymer chains and its impact on the inter-chain charge transport property. Here, by using the combination of steady-state X-ray absorption spectroscopy, optical transient absorption spectroscopy, X-ray transient absorption spectroscopy, and electrochemical impedance spectroscopy, we show that the linear ligands (An Ph , An Me , and An H ) with different degrees of steric groups (Ph > Me > H) introduced at the 9 and 10 position of anthracene can alter the stacking of the polymer chains and thus impact their crystallinity, charge separation, and charge transport property, which in turn impacts their photocatalytic performance for hydrogen evolution reaction.

1-D-polymer↗
DOE OSTI2026

Intrinsically Conductive {pi}‑d Conjugated Layers with Co–N4 Active Sites for Efficient Nitrate Electrocatalysis and Zinc-Nitrate Batteries

Electrochemical synthesis of ammonia from nitrate has been extensively investigated as a potential alternative to the energy-intensive Haber-Bosch process. This approach not only operates under ambient conditions but also simultaneously removes nitrate contaminants while producing ammonia as a value-added product. However, the ongoing quest lies in designing an efficient electrocatalyst that achieves a high ammonia yield rate, high selectivity, and long-term stability. Herein, we report the outstanding performance of a Co–N4 coordinated π-d layered Co3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) in nitrate electrocatalysis. The unique combination of abundant Co–N4 active sites and superior electrical conductivity enables significant electrocatalytic activity, delivering a maximum ammonia yield rate of 56.8 mg cm–2 h–1 at −0.8 V vs RHE and a Faradaic efficiency of ∼91% at −0.4 V vs RHE. Mechanistic analysis reveals that alkaline conditions accelerate water dissociation to generate adsorbed hydrogen intermediates (H*), which are utilized by Co–N4 sites to drive the stepwise hydrogenation of nitrate to ammonia while suppressing competing hydrogen evolution reaction (HER) pathways. Furthermore, integration of this catalyst into a zinc-nitrate battery resulted in a maximum power density of 5.3 mW cm–2 and an open-circuit potential of ∼1.45 V. These results highlight the potential of π-d conjugated Co–N4 materials as an efficient catalyst for both environmental remediation and energy conversion.

Namvar, shahrirar↗
DOE OSTI2026

Syngas Production at Si Hybrid Photoelectrodes Modified with Re(I) and Mn(I) Tricarbonyl Phenanthroline Complexes Containing Reactive Aryl Azide Groups

We installed molecular CO 2 reduction (CO 2 R) catalysts directly onto Si (photo)electrodes. The highly reactive M(5-azido-1,10-phenanthroline)(CO) 3 X (where M = Mn or Re, X = Br or Cl) complexes readily bubbled when dissolved in polar organic solvents, in both the presence and absence of an ultraviolet light source. When placed on hydrogen-terminated Si (H-Si) and native silicon oxide (SiOx), similar amounts of the complex were attached to the surface under illumination (367 nm, 50–200 mW/cm 2 ) or in the dark. Surprisingly, these films revealed submonolayer coverages instead of the multilayered structures we expected. DFT analyses support monolayer formation, showing that the triplet-state nitrene of the complex is more energetically favorable than the singlet state. Using controlled-potential electrolysis experiments, we showed that Re- and Mn-containing films on pSi photoelectrodes generated small amounts of CO when exposed to 1 atm of CO 2 and 1 sun illumination. These amounts of CO were an order of magnitude greater than control surfaces, producing 5.59 × 10 –7 mol CO/h for Re(az-phen) and 7.83 × 10 –7 mol CO/h for Mn(az-phen) films. Much of the charge passed at the pSi electrodes was consumed by the competing hydrogen evolution reaction, which we attribute to the low molecular coverage and the presence of native oxide on the electrode surface after attachment. Finally, this work demonstrates the feasibility of reacting azide-containing ligands with Si surfaces. Still, it highlights the need for alternative ligand structures and reaction conditions to form multilayer films.

azides↗
DOE OSTI2020

Electrokinetic Analysis of Poorly Conductive Electrocatalytic Materials

While many factors can influence the activity of the electrochemical interface at atomic and molecular levels, the electron and ion transport have a big impact on the overall electrochemical performance. Here, we investigate how electrical resistance (conductivity) of the electrode affects the measured electrocatalytic activity using the hydrogen evolution reaction as a model reaction. We clearly demonstrate the effect of the poor electronic conductivity of MoS 2 on the electrochemical performance, as both values of the exchange current density as well as the Tafel slope depend on the level of utilization of the active material and the ohmic losses. A quantitative analysis using the composite electrode model is provided, showing the importance of the experimental conditions and good control of electrode/electrolyte system for the proper evaluation and comparison of electrocatalysts’ kinetic parameters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Ternary Phosphides Ba M 2 P 2 : Tailoring Crystal and Electronic Structures Enables Highly Efficient HER Electrocatalysis

Binary transition metal phosphides and their solid solutions have emerged as promising hydrogen evolution reaction (HER) catalysts. Although many research endeavors have adopted strategies to vary compositions to optimize catalytic performance, they mainly focus on binary structures, which represent only a small fraction of the abundant phase space of structure types among transition metal phosphides. Here, the largely unexplored class of ternary and multinary ordered phosphides in catalysis comprises two or more metals with quite different chemical nature, concealing the structure–property relationships essential for advancing catalyst design. Here, we explored phosphides crystallizing in one of the most abundant ordered intermetallic structure types, —the ThCr 2 Si 2 type, —where square nets of 3d transition metal M and P atoms are separated by layers of electropositive Ba cations. Four ternary BaM 2 P 2 (M = Fe, Fe/Cu, Fe/Ni, Ni) catalysts were synthesized and characterized. BaNi 2 P 2 showed high HER activity in acidic electrolyte, which required an overpotential, η 10 , of only 62 mV to drive current density j = –10 mA/cm 2 and high stability with a potential drop rate of 0.25 mV/h. BaNi 2 P 2 outperformed other Ni-based catalysts, such as Ni 2 P and Ni 5 P 4 . Notably, at current densities above –170 mA/cm 2 , BaNi 2 P 2 outperformed the standard Pt electrode measured under identical conditions. Electronic structure analysis revealed a volcano-type activity trend among the four BaM 2 P 2 catalysts based on their d-band center positions, highlighting the role of electropositive Ba cations in shifting the Ni-3d orbitals into an optimal position.

BaNi2P2↗
DOE OSTI2025

Anion Exchange Membrane Water Electrolysis Using a Catalyst-Coated Membrane Cathode

A catalyst-coated membrane (CCM) approach to electrode fabrication for high pH water electrolysis offers enhanced interfacial contact between the catalyst layer and the membrane surface in comparison to the catalyst-coated substrate (CCS) electrode configuration. The CCM facilitates enhanced ionic and water transport between the cathode and the anion exchange membrane (AEM). This advantage is particularly significant with AEM water electrolysis (compared to proton exchange membrane water electrolysis) because the cathode typically operates under dry conditions and relies solely on diffusive water transport across the AEM from the liquid-fed anode. This study presents a direct performance comparison between CCS and CCM cathode configurations using identical hydrogen evolution reaction (HER) catalysts and other components. The use of a pseudo-reference electrode integrated into the membrane electrode assembly enabled detailed analysis of the CCM cathode polarization behavior. Surface characterization provided insight into the degradation mechanisms associated with the CCM configuration. Optimization of the cathode ionomer cross-link density improved both the cathode polarization performance and the electrolysis device durability. Further optimization of the HER catalyst loading in the CCM cathode resulted in additional gains in the electrolysis efficiency. Collectively, these findings offer valuable guidance for the design and fabrication of high-performance, durable AEM electrolysis CCMs.

Water electrolysis↗
DOE OSTI2025

Plasma-Assisted Surface Nitridation of Proton Intercalatable WO 3 for Efficient Electrocatalytic Ammonia Synthesis

Electrocatalytic nitrogen reduction (eNRR) offers a green pathway for the production of NH 3 from N 2 and H 2 O under ambient conditions. Transition metal oxynitrides (TMO x N y ) are among the most promising catalysts but face challenges in achieving a high yield and faradaic efficiency (FE). This work develops a hybrid WO x N y /WO 3 catalyst with a unique heterogeneous interfacial complexion (HIC) structure. This design enables in situ generation and delivery of highly active hydrogen atoms (H*) in acidic electrolytes, promoting nitrogen hydrogenation and the formation of nitrogen vacancies (Nv) on the WO x N y surface. This significantly enhances the selectivity of eNRR for NH 3 synthesis while suppressing the hydrogen evolution reaction (HER). A simple two-step fabrication process─microwave hydrothermal growth followed by plasma-assisted surface nitridation─was developed to fabricate the designed catalyst electrode, achieving an NH 3 yield of 3.2 × 10 –10 mol·cm –2 ·s –1 with 40.1% FE, outperforming most TMN/TMO x N y electrocatalysts. Multiple control experiments confirm that the eNRR follows an HIC-enhanced Mars–van Krevelen (MvK) mechanism.

Catalysts↗
DOE OSTI2025

Red Light-Powered Nanowire Photochemical Diodes for Unassisted Hydrogen Evolution and Glycerol Valorization

Artificial photosynthesis via unassisted photochemical diodes is a promising approach for generating solar fuels. However, photoelectrochemical systems often degrade under solar diurnal cycling, and reliance on solar insolation exacerbates land use. Narrow-band LED illumination offers continuous and constant operation, enabling the vertical integration of stable photochemical diodes. In this study, 740 nm red light was investigated as the illumination source for silicon-based photochemical diodes integrating the hydrogen evolution reaction with the glycerol oxidation reaction (GOR), where replacing the oxygen evolution reaction with GOR increases attainable bias-free photocurrents. Increasing photovoltages, saturation current densities, and power conversion efficiencies were observed with increasing incident red light intensity. Under a red light intensity of 60 mW cm –2 , these systems are stable above 7.5 mA cm –2 for 6 days with periodic electrolyte refreshing. In conclusion, these results offer a promising prospect for red light-powered photochemical diodes that integrate other significant reduction reactions, such as CO 2 reduction.

Alcohols↗