Conversion of inert N
2
molecules into NH
3
via electrochemical methods is an environmentally friendly alternative to replace the traditional Haber-Bosch process. However, the development of highly ...efficient catalyst is still challenging. Herein, we report a density functional theory (DFT) based high-throughput screening to investigate the potential of 23 atomic transition metals (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, W, Pt and Au) supported on phosphorene monolayer as electrocatalyst for nitrogen reduction reaction (NRR). Our theoretical results demonstrate that V single atom anchoring on phosphorene monolayer exhibits good thermal stability, selectivity and excellent catalytic activity with a low overpotential of 0.18 V. Importantly, rational design principles and electronic descriptor between the intrinsic electronic properties and activation barrier have been developed. Our work offers a new promising noble metal-free catalyst for NRR and reveals profound insights into the activity origin to guide further design.
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•Co-decorated N-doped graphene is a promising material for hydrogen gas storage.•The transition point of chemisorption/physisorption of hydrogen gas occurs under 8% strain.•Almost all ...hydrogen gas can be released by applying 10% strain.•The usable storage capacity is 6.00% at low pressure and room temperature.
As a feasibility study for hydrogen storage, the adsorption behavior of H2 on transition metal-decorated N-doped graphene is systematically investigated by density functional theory and the adsorption isotherm is used to predict to practical capacity at realistic condition by grand canonical partition function. The biaxial strain is proposed to be a reversible switch for hydrogen storage. Our computational results suggest that Co-decorated N-doped graphene is a highly promising material for hydrogen gas storage with good thermal stability and excellent gravimetric density. Additionally, the adsorption of H2 is sensitive to the biaxial tensile strain, and the transition point of chemisorption/physisorption occurs under 8% strain. By applying 10% strain for desorption, the storage capacity can be effectively improved to 6.00 wt% (i.e. 19% enhancement) at low pressure and room temperature. Our findings not only reveal the feasibility of a tunable material for hydrogen storage, but also provide a new strategy to control the performance for hydrogen storage by biaxial tensile strain.
Using self-assembly gold nanoislands (SAM-AuNIs) functionalized by poly(m-phenylenediamine-co-aniline-2-sulfonic acid) (poly(mPD-co-ASA)) copolymer nanoparticles as specific receptors, a highly ...sensitive localized surface plasmon resonance (LSPR) optochemical sensor is demonstrated for detection of trace lead cation (Pb(II)) in drinking water. The copolymer receptor is optimized in three aspects: (1) mole ratio of mPD:ASA monomers, (2) size of copolymer nanoparticles, and (3) surface density of the copolymer. It is shown that the 95:5 (mPD:ASA mole ratio) copolymer with size less than 100 nm exhibits the best Pb(II)-sensing performance, and the 200 times diluted standard copolymer solution contributes to the most effective functionalization protocol. The resulting poly(mPD-co-ASA)-functionalized LSPR sensor attains the detection limit to 0.011 ppb toward Pb(II) in drinking water, and the linear dynamic range covers 0.011 to 5000 ppb (i.e., 6 orders of magnitude). In addition, the sensing system exhibits robust selectivity to Pb(II) in the presence of other metallic cations as well as common anions. The proposed functional copolymer functionalized on AuNIs is found to provide excellent Pb(II)-sensing performance using simple LSPR instrumentation for rapid drinking-water inspection.
Designing highly efficient and low-cost electrocatalysts for oxygen evolution reaction is important for many renewable energy applications. In particular, strain engineering has been demonstrated as ...a powerful strategy to enhance the electrochemical performance of catalysts; however, the required complex catalyst preparation process restricts the implementation of strain engineering. Herein, we report a simple self-template method to prepare hierarchical porous Co
3
O
4
nanowires (PNWs) with tunable compressive strain via thermal-oxidation-transformation of easily prepared oxalic acid-cobalt nitrate (Co(NO
3
)
2
) composite nanowires. Based on the complementary theoretical and experimental studies, the selection of proper solvents in the catalyst preparation is not only vital for the hierarchical structural evolution of Co
3
O
4
but also for regulating their compressive surface strain. Because of the rich surface active sites and optimized electronic Co d band centers, the PNWs exhibit the excellent activity and stability for oxygen evolution reaction, delivering a low overpotential of 319 mV at 10 mA·cm
−2
in 1 M KOH with a mass loading 0.553 mg·cm
−2
, which is even better than the noble metal catalyst of RuO
2
. This work provides a cost-effective example of porous Co
3
O
4
nanowire preparation as well as a promising method for modification of surface strain for the enhanced electrochemical performance.
Highlights
The strong interaction between Ti
3
C
2
S
x
and FeN
4
species induces the central metal Fe(II) in FeN
4
species with intermediate spin state transferred to high spin state, in which the ...latter is favorable to initiate the reduction of oxygen.
This strong interaction induces a remarkable Fe 3
d
electron delocalization with
d
band center upshift, boosting oxygen-containing groups adsorption on FeN
4
species and oxygen reduction reaction kinetics.
The resulting FeN
4
–Ti
3
C
2
S
x
with FeN
4
moieties in high spin state exhibits high half-wave potential of 0.89 V vs. RHE and high limiting current density of 6.5 mA cm
−2
, enabling wearable zinc–air battery showing a good discharge performance with a maximum power density of 133.6 mW cm
−2
.
Transition metal–nitrogen–carbon materials (M–N–Cs), particularly Fe–N–Cs, have been found to be electroactive for accelerating oxygen reduction reaction (ORR) kinetics. Although substantial efforts have been devoted to design Fe–N–Cs with increased active species content, surface area, and electronic conductivity, their performance is still far from satisfactory. Hitherto, there is limited research about regulation on the electronic spin states of Fe centers for Fe–N–Cs electrocatalysts to improve their catalytic performance. Here, we introduce Ti
3
C
2
MXene with sulfur terminals to regulate the electronic configuration of FeN
4
species and dramatically enhance catalytic activity toward ORR. The MXene with sulfur terminals induce the spin-state transition of FeN
4
species and Fe 3
d
electron delocalization with d band center upshift, enabling the Fe(II) ions to bind oxygen in the end-on adsorption mode favorable to initiate the reduction of oxygen and boosting oxygen-containing groups adsorption on FeN
4
species and ORR kinetics. The resulting FeN
4
–Ti
3
C
2
S
x
exhibits comparable catalytic performance to those of commercial Pt-C. The developed wearable ZABs using FeN
4
–Ti
3
C
2
S
x
also exhibit fast kinetics and excellent stability. This study confirms that regulation of the electronic structure of active species via coupling with their support can be a major contributor to enhance their catalytic activity.
The development of effective metal-free electrocatalytic for hydrogen evolution reaction (HER) to substitute precious Pt based catalyst has attracted massive research interests. Herein, we report a ...density functional theory (DFT) investigation on activation and optimization of a new metal-free two-dimensional (2D) material, namely, phosphorus carbide (β-PC) monolayer as efficient HER electrocatalysts by applying reasonable C-vacancies and strain. Our theoretical results show that the C-vacancies introduce in-gap states, thus significantly increase the electrical conductance and hydrogen binding strength, which are favorable for HER process. The hydrogen adsorption free energies (ΔGH) can be effectively controlled by strain and C-vacancies concentration. Appropriate combinations of strain and C-vacancies concentration can achieve optimal conditions of ΔGH ≈ 0 and excellent exchange current density, suggesting a superior catalytic activity comparable to Pt. Moreover, the physico-chemical origin of defect and strain on nonmetal-H bonding were rationalized by establishing a linear relationship between hydrogen adsorption strength and the intrinsic electronic structure of β-PC. Our work offers a new promising metal-free catalyst for HER and reveals profound insights into the bonding mechanisms of nonmetal-H bond to guide the atomic design of more efficient metal-free electrocatalysts.
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•Phosphorus Carbide (β-PC) monolayer is proposed as an efficient metal-free electrocatalyst for HER.•The catalytic activity of β-PC monolayer could be fine-tuned by C-vacancies concentration and strain.•Optimal conditions can be achieved with ΔGH≈0 and excellent i0, which are both comparable to those of Pt.•The electronic descriptors of strain and defect on nonmetal-H bond are investigated.
The effect of several potential factors on the desorption behavior of saturated superabsorbent polymers (SAPs) in concrete was studied by simulating the internal saline concentration, alkalinity, and ...relative humidity. Results indicate that the desorption of SAP is mainly decided by osmotic pressure and humidity gradient. The desorption process of SAP is divided into three stages: the leading factor is the osmotic pressure during the first stage; humidity gradient during the third stage; and a relatively low-level combination of these two factors during the second stage. At the same time, the desorption is not decided by pH value, and the factor with the most effect is the osmotic pressure. The water release rate R.sub.t of saturated SAP influenced by humidity shows the following trends: R.sub.t indicates a clear linear trend as a function of time, and an approximate logarithm correlation exists between Rt and the relative humidity (R.sub.t = A * ln(RH) + B). Keywords: desorption; different stages; humidity gradient; osmotic pressure; pH value; superabsorbent polymers.
Density functional theory (DFT) calculations have been performed to investigate the electronic properties of pristine monolayer MoS2 and various transition-metal (TM) (Ni, Pt, Ti and Pd) doped MoS2 ...as well as the adsorption of formaldehyde on these monolayer 2D structures. It was found that the CH2O adsorption energy (0.11 eV) on monolayer MoS2 was very weak, indicating that pristine MoS2 is insensitive to formaldehyde (CH2O). However, the adsorption of CH2O on monolayer TM-MoS2 shows relatively high affinity. Thus, TM-doping can substantially improve the sensitivity towards CH2O. In order to investigate the mechanism of adsorption, the electronic properties such as molecular projected density of states and differential charge transfer were calculated. The results showed that the adsorption on Ti-doped monolayer MoS2 (1.59 eV) is very promising with the most stable adsorption. Both differential charge transfer and ab initio molecular dynamic were used to investigate the adsorption mechanism. The ab initio molecular dynamic at 500 K was performed using the Car-Parrinello method. The most stable configuration shows the highest adsorption energy and CH2O can be adsorbed even at 500 K. These suggest that Ti-doped monolayer MoS2 would be a feasible material for CH2O removal at room temperature.
•Ti-MoS2, Pt-MoS2 or Ni-MoS2 is n-type semiconductor while Pd-MoS2 is p-type.•The CH2O molecule is chemisorbed on Ni-, Pt-, Ti- and Pd-doped MoS2.•The adsorption energy of CH2O on MoS2 is increased after doping. CH2O has the strongest affinity to Ti-doped MoS2.•The CH2O molecule is adsorbed on Ti-doped MoS2 with Ti-O and Ti-C keeping its bond characteristics from 100 K to 500 K.
The development of low-cost and high-performance electrocatalyst-supporting materials is desirable and necessary for the ethanol oxidation reaction (EOR). Here, we report a facile and universal ...template-free approach for the first time to synthesize three-dimensional (3D) flower-like ionic liquid-functionalized graphene (IL-RGO). Then, the crystalline Pd nanoparticles were anchored on IL-RGO by a simple wet chemical growth method without a surfactant (denoted as Pd/IL-RGO). In particular, the IL is conducive to form a 3D flower-like structure. The optimized Pd/IL-RGO-2 presents a much-promoted electrocatalytic performance toward the EOR compared with commercial Pd/C catalysts, which is mainly derived from the grafted IL on RGO and the unique 3D flower-like structure. In detail, the IL can control, stabilize, and disperse the Pd nanocrystals as well as serving as the solvent and electrolyte in the microenvironment of the EOR, and the 3D flower-like structure endows the Pd/IL-RGO with high surface areas and rich opened channels, thereby kinetically accelerating the charge/mass transfers. Furthermore, density functional theory calculations reveal that the strong electronic interaction between Pd and IL-RGO generates a downshift of d center for Pd and thereby enhances the durability toward CO-like intermediates and electrocatalytic reaction kinetics.
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•Metal-Nx embedded on graphene with double vacancies are more stable for CO2RR.•Adsorption energies of COOH and CO can be used as descriptors for CO2RR to CO.•Co-N4, Ni/Pd/Pt-N1, and ...Rh-N4 show high CO2RR activities but low selectivity.•Ni-N4 is the most effective site for CO production.•Fe-N4 is favorable for *CO further reduction at low electrode potential.
Electrochemical CO2 reduction reaction (CO2RR) is an effectivestrategy for CO2 conversion and clean fuel generation. Diverse nitrogen-doped carbon-supported transition metal (M-N-C) have been proved as favorable catalysis materials for CO2RR, especially for CO production. Herein, density functional theory is performed to investigate the CO2RR mechanisms over M-Nx-C with twelve types of transition metal centers. Fe-, Co-, Ni-, Cu-, Rh-, Pd-, Ir-, and Pt-Nx embedded on graphene with double vacancies are relatively stable structures contributing to electrocatalysis operation. The adsorption energies of COOH and CO, which are the reaction intermediates during CO2RR, are linearly related and can be used as a descriptor for CO production. Moderate adsorption strengths of CO and COOH are favorablefor CO generation with low limiting potential. Co-N4, Ni-N1, Pd-N1, Pt-N1, and Rh-N4 are the most active sites for CO2RR by thermodynamics analysis. However, the discussion on competition between CO2RR and hydrogen evolution reaction (HER) indicates that these sites show low selectivity. Considering both CO2RR selectivity and activity, Ni-N4 site is proved to be the most effective site for CO production among all the M-Nx sites. It is also noted that Fe-N4 is more favorable to further reduction towards *CO with the products of CH3OH and CH4.
