arXiv subjects

Pedro H. Souza

Publications and source records attributed to Pedro H. Souza.

6 recordsLinked to original sources

arXiv2026

Understanding the Oxygen Reduction Reaction and Oxygen Evolution Reaction in Metal Intercalated Biphenylene Bilayers

We conducted an {\it ab initio} study of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in metal-encapsulated biphenylene bilayers, B/M/B, with M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Ru, W, Os and Pt. In most systems, the intercalated metal sits at the square carbon sites (C$^{468}$) of the biphenylene lattice. Using a computational hydrogen electrode approach, we evaluated the reaction energetics at these active sites. Several B/M/B systems show competitive ORR and OER performance. Among the investigated systems, Cu, Pt, Ru, and Mn exhibit the lowest ORR overpotentials of 0.42, 0.44, 0.50, and 0.56 V, respectively, while Fe is identified as the most active catalyst for OER with an overpotential of 0.44 V. To understand the catalytic trends, we looked at the electronic structure through the metal $d-$band centers, the C$^{468}$ $p_z-$band centers, and the corresponding orbital charge populations. The band centers did not give a simple polynomial dependence on the overpotentials, though they did point to favorable electronic ranges for the best catalysts. The $d-$orbital charge population of the encapsulated metal, however, correlated most clearly with activity-especially for OER-yielding volcano-type plots. From these, B/Fe/B emerges as the best OER catalyst, while B/Mn/B lies closest to the ORR optimum. The $p-$orbital population at the active carbon site also captures the main trends, albeit less strongly. Overall, these results show that straightforward electronic descriptors can predict catalytic behavior in metal-encapsulated biphenylene bilayers and guide the search for efficient catalysts where the carbon framework itself drives the reactivity.

cond-mat.mtrl-sci↗

arXiv2026

Metal-Coordination Effects on the Stability and ORR/OER Activity of Layered Organometallic Single-Atom Catalysts: A Theoretical Study

Organometallic layered materials have emerged as promising single-atom catalysts for oxygen reduction and evolution reactions, but their practical use has been limited by insufficient electrochemical stability. Here, we present a density functional theory study clarifying the relationship between catalytic activity and stability in organometallic single-atom catalysts with metal-N$_4$ (MN$_4$) and metal-O$_4$ (MO$_4$) coordination. We compare graphene-embedded MN$_4$ motif and phthalocyanine-like frameworks with MO$_4$-coordination frameworks, including M$_4$(OHPTP)$_2$ and M$_3$(HHTP)$_2$ (M = Mn, Fe, Co, Ni, Cu, Zn). Stability is assessed by surface Pourbaix analysis, while activity is evaluated using the computational hydrogen electrode method. MN$_4$ systems show competitive overpotentials but suffer strong pH-dependent instability. In contrast, MO$_4$ frameworks exhibit enhanced robustness across wide pH ranges while maintaining good catalytic performance. A proposed stability descriptor enables direct comparison across systems, identifying MO$_4$ coordination structures, particularly M$_4$(OHPTP)$_2$ (M = Zn, Co) as optimal for balancing activity and stability in practical electrocatalysis.

cond-mat.mtrl-sci↗

arXiv2023

Bridging Borophene and Metal Surfaces: Structural, Electronic, and Electron Transport Properties

Currently, solid interfaces composed of two-dimensional materials (2D) in contact with metal surfaces (m-surf) have been the subject of intense research, where the borophene bilayer (BBL) has been considered a prominent material for the development of electronic devices based on 2D platforms. In this work, we present a theoretical study of the energetic, structural, and electronic properties of the BBL/m-surf interface, with m-surf = Ag, Au, and Al (111) surfaces, and the electronic transport properties of BBL channels connected to the BBL/m-surf top contacts. We find that the bottom-most BBL layer becomes metalized, due to the orbital hybridization with the metal surface states, resulting in BBL/m-surf ohmic contacts, meanwhile, the inner and top-most boron layers kept their semiconducting character. The net charge transfers reveal that BBL has become $n$-type ($p$-type) doped for m-surf = Ag, and Al (= Au). A thorough structural characterization of the BBL/m-surf interface, using a series of simulations of the X-ray photoelectron spectra, shows that the formation of BBL/m-surf interface is characterized by a redshift of the B-$1s$ spectra. Further electronic transport results revealed the emergence of a Schottky barrier between 0.1 and 0.2\,eV between the BBL/m-surf contact and the BBL channels. We believe that our findings are timely, bringing important contributions to the applicability of borophene bilayers for developing 2D electronic devices.

cond-mat.mtrl-sci↗

arXiv2022

Oxidation of 2D electrenes: structural transition and the formation of half-metallic channels protected by oxide layers

Based on first-principles calculations we performed a systematic study of the energetic stability, structural characterization, and electronic properties of the fully oxidized $A_{2}B$, electrenes, with the following combinations, (i) $A$=Ca, Sr, and Ba for $B$=N; (ii) $A$=Sr and Ba for $B$=P; and Y$_{2}$C, and Ba$_{2}$As. We have considered one side oxidation of single layer electrenes $(O/A_{2}B)$, and two side oxidation of bilayer electrenes $(O/(A_{2}B)_{2}/O)$. We show that the hexagonal lattice of the pristine host is no longer the ground state structure in the oxidized systems. Our total energy results reveal an exothermic structural transition from hexagonal to tetragonal (h$\rightarrow$t) geometry, resulting in layered tetragonal structures [$(AOAB)^{t}$, and $(AO(AB)_{2}AO)^{t}$]. Phonon spectra calculations and molecular dynamic simulations show that the $O/A_{2}B$, and $O/(A_{2}B)_{2}/O$ systems, with $A$=Ba, Ca, Sr, and $B$=N, become dynamically and structurally stable upon such a h$\rightarrow$t transition. Further structural characterizations were performed based on simulations of the near edge X-ray absorption spectroscopy at the nitrogen K-edge. Finally, the electronic structure calculations and transport calculations reveal the formation of half-metallic bands spreading out through the $A$N layers, which are shielded by oxide $A$O sheets. These findings indicate that $(AOAB)^{t}$, and $(AO(AB)_{2}AO)^{t}$, (with $B$=N) are quite interesting platforms for application in spintronics; since the half-metallic channels along the $A$N or $(A\text{N})_2$ layers (core) are protected against the environment conditions by the oxidized $A\text{O}$ sheets (cover shells).

cond-mat.mtrl-sci↗

arXiv2020

Structural Transition in Oxidized Ca$_2$N Electrenes: CaO/CaN 2D heterostructures

Based on first-principles calculations we show that the oxidation of ultrathin films of Ca$_2$N electrides, electrenes, drives a hexagonal$\rightarrow$tetragonal structural transition. The ground state configuration of the oxidized monolayer (ML) and bilayer (BL) systems can be viewed as CaO/CaN and CaO/(CaN)$_2$/CaO two dimensional (2D) heterostructures. In both systems, we found nearly free electron (NFE) states lying near the vacuum level, and the spatial projection reveals that they are localized above the oxidized CaO surface. Focusing on the magnetic properties, we find that the nitrogen atoms of the oxidized Ca$_2$N becomes spin-polarized ($\sim$1 $μ_{\rm B}$/N-atom); where (i) the ferromagnetic and the anti-ferromagnetic phases are nearly degenerated in the ML system, CaO/CaN, while (ii) there is an energetic preference for the ferromagnetic phase in CaO/(CaN)$_2$/CaO. We show that such a FM preference can be strengthened upon mechanical compression. Further electronic structure calculations reveal that the FM CaO/Ca$_2$N/CaO presents half-metallicity, where the metallic channels project (predominantly) on the N-$2p_{x,y}$ orbitals. In addition to the total energy results, molecular dynamic and phonon spectra calculations have been done in order to verify its thermal and structural stabilities. Those findings suggest that CaO/Ca$_2$N/CaO is a quite interesting, and structurally stable, 2D FM heterostructure characterized half-metallic bands sandwiched by NFE states lying on the oxidized surfaces.

cond-mat.mtrl-sci↗

arXiv2018

Curved non-interacting two-dimensional electron gas with anisotropic mass

In the da Costa's thin-layer approach, a quantum particle moving in a 3D sample is confined on a curved thin interface. At the end, the interface effects are ignored and such quantum particle is localized on a curved surface. A geometric potential arises and, since it manifests due to this confinement procedure, it depends on the transverse to the surface mass component. This inspired us to consider, in this paper, the effects due to an anisotropic effective mass on a non-interacting two dimensional electron gas confined on a curved surface, a fact not explored before in this context. By tailoring the mass, many investigations carried out in the literature can be improved which in turns can be useful to better designing electronic systems without modifying the geometry of a given system. Some examples are examined here, as a particle on helicoidal surface, on a cylinder, on a catenoid and on a cone, with some possible applications briefly discussed.

cond-mat.mes-hall↗