Heteroatom decorated C2N monolayer for gas-sensing application: Insight from first-principles

Development of novel gas-sensing materials is essential to high-performance gas sensors for monitoring target gases in industrial production and environmental protection. Herein, we investigate two types of the heteroatom-decorated C2N monolayer, denoted as M@C2N (M = Mn and Ni) and B-C2N, for their gas-sensing functionality toward seven small gaseous molecules (H2, O2, N2, CO, CO2, NH3, and H2O). The key gas-sensing characteristics concerning chemiresistive (CR) and field-effect transistor (FET) gas sensing have been thoroughly explored. The results show that Mn@C2N and Ni@C2N can work as either CR or FET gas-sensing materials for detecting H2, O2, N2, CO, CO2, NH3, and H2O, whereas B-C2N can work as a disposable gas sensor for O2, H2O, and NH3. Mn@C2N and Ni@C2N are the most selective toward O2 and NH3, followed by CO and H2O in an oxygen- and ammonia-free environment, while B-C2N is the most selective toward H2O and NH3. More importantly, the adsorption strength of target molecule plays a critical role in gas-sensing mechanism as well as selectivity, recovery time, and sensitivity. This study offers theoretical perspectives on 2D hybrid carbon-based nanomaterials for efficient gas sensing.

Linear Scaling Relationships for Furan Hydrodeoxygenation over Transition Metal and Bimetallic Surfaces

Brønsted-Evans-Polanyi (BEP) and transition-state-scaling (TSS) relationships have become valuable tools for the rational design of catalysts for complex reactions like hydrodeoxygenation (HDO) of bio-oil (containing heterocyclic and homocyclic molecules). In this work, BEP and TSS relationships are developed for all the elementary steps of furan activation (C and O hydrogenation and CHx -OHy scission, for both ring and open-ring intermediates) to oxygenates, ring-saturated compounds and deoxygenated products on the most stable facets of Ni, Co, Rh, Ru, Pt, Pd, Fe and Ir surfaces using Density Functional Theory (DFT) calculations. Furan ring opening barriers were found to be facile and strongly dependent on carbon and oxygen binding strength on the investigated surfaces. Our calculations suggest linear chain oxygenates form on Ir, Pt, Pd and Rh surfaces due to their low hydrogenation and high CHx -OHy scission barriers, while deoxygenated linear products are favoured on Fe and Ni surfaces due to their low CHx -OHy scission and moderate hydrogenation barriers. Bimetallic alloy catalysts were also screened for their potential HDO activity and PtFe catalysts were found to significantly lower the ring opening and deoxygenation barriers relative to the corresponding pure metals. The developed BEPs for monometallic surfaces can be extended to estimate the barriers on bimetallic surfaces for ring opening and ring hydrogenation reactions but fails to predict the barriers for open-ring activation reactions due to the change in transition state binding sites on the bimetallic surface. The obtained BEP and TSS relationships can be used to develop microkinetic models for facilitating accelerated catalyst discovery for HDO.

Synergistic effect of diatomic Mo-B site confined in graphene-like C2N enables electrocatalytic nitrogen reduction via novel mechanism

Structural modulation of the active site with atomic-level precision is of great importance to meet the activity and selectivity challenges that electrocatalysts are commonly facing. In this work, we have designed a metal (M)-nonmetal diatomic site embedded in graphene-like C₂N (denoted as Mo-B@C₂N), where the electrocatalytic N₂ reduction reaction (eNRR) was thoroughly explored using density functional theory combined with the computational hydrogen electrode method. Compared to M-M diatomic sites, the Mo-B site can generate a pronounced synergistic effect that led to eNRR proceeding via a novel quasi-dissociative reaction mechanism that has not been reported relative to the conventional enzymatic, consecutive, distal, and alternating associative mechanism. This newly uncovered mechanism in which N-N bond scission takes place immediately after the first proton-coupled electron transfer (PCET) step (i.e., *NH-*N + H⁺ + e^- → *NH₂*N) has demonstrated much advantage in the PCET process over the four conventional mechanism in terms of thermodynamic barrier, except that the adsorption of side-on *N₂ seemed thermodynamically unfavorable (ΔG_ads = 0.61 eV). Our results have revealed that the activation of the inert N≡N triple bond is dominated by the π*-backdonation mechanism as a consequence of charge transfers from both the B and Mo sites and, unexpectedly, from the substrate C₂N itself as well. Moreover, the hybrid Mo-B diatomic site demonstrated superior performance over either the Mo-Mo or B-B site for driving eNRR. Our study could provide insight into the delicate relationships among atomic site, substrate, and electrocatalytic performance.

Recent Advances in Anode Electrocatalysts for Direct Formic Acid Fuel Cells - Part I - Fundamentals and Pd Based Catalysts

Direct formic acid fuel cells (DFAFCs) have gained immense importance as a source of clean energy for portable electronic devices. It outperforms other fuel cells in several key operational and safety parameters. However, slow kinetics of the formic acid oxidation at the anode remains the main obstacle in achieving a high power output in DFAFCs. Noble metal-based electrocatalysts are effective, but are expensive and prone to CO poisoning. Recently, a substantial volume of research work have been dedicated to develop inexpensive, high activity and long lasting electrocatalysts. Herein, recent advances in the development of anode electrocatalysts for DFAFCs are presented focusing on understanding the relationship between activity and structure. This review covers the literature related to the electrocatalysts based on noble metals, non-noble metals, metal-oxides, synthesis route, support material, and fuel cell performance. The future prospects and bottlenecks in the field are also discussed at the end.

Tetrahedral W4cluster confined in graphene-like C2N enables electrocatalytic nitrogen reduction from theoretical perspective

Exploring the format of active site is essential to further the understanding of an electrocatalyst working under ambient conditions. Herein, we present a DFT study of electrocatalytic nitrogen reduction (eNRR) on W₄tetrahedron embedded in graphene-like C₂N (denoted as W₄@C₂N). Our results demonstrate that N-affinity of active sites on W₄dominate over single-atom site, rendering *NH₂ + (H⁺ + e^-) →*NH₃invariably the potential-determining step (PDS) of eNRR via consecutive or distal route (U_L = -0.68 V) to ammonia formation. However, *NHNH₂ + (H⁺ + e^-) →*NH₂NH₂has become the PDS (U_L = -0.54 V) via enzymatic route towards NH₂NH₂formation and thereafter desorption, making W₄@C₂N a potentially promising catalyst for hydrazine production from eNRR. Furthermore, eNRR is competitive with hydrogen evolution reaction (U_L = -0.78 V) on W₄@C₂N, which demonstrated sufficient thermal stability and electric property for electrode application.

The role of Ni sites located in mesopores for the selectivity of anisole hydrodeoxygenation

A highly-dispersed Ni catalyst with an increased number of Ni sites selectively distributed in the mesopores of HBEA has been developed and applied in anisole hydrodeoxygenation (HDO) in a continuous-flow...

Single-, double-, and triple-atom catalysts on graphene-like C2N enable electrocatalytic nitrogen reduction: insight from first principles

The *NHx intermediates on Mn@C2N are highly stable for n = 3 and unstable for n = 1, rendering Mn@C2N as the optimal candidate for driving the eNRR owing to its moderate binding with NHx (x = 0, 1, 2, 3).

Mo single atoms in the Cu(111) surface as improved catalytic active centers for deoxygenation reactions

The surface Mo-doped Cu(111) catalyst feature improved performance towards deoxygenation reactions, acting as a single-atom alloy capable of breaking Brønsted–Evans–Polanyi relations for carbonyl bond scissions.

Stepped M@Pt(211) (M = Co, Fe, Mo) single-atom alloys promote the deoxygenation of lignin-derived phenolics: mechanism, kinetics, and descriptors

HDO of lignin-derived phenolics on stepped M@Pt(211) (M = Co, Fe, Mo) single-atom alloy was computationally explored. Either C–O bond length or *OH binding energy was confirmed as an effective catalytic descriptor for predicting HDO performance.