Modulating the Local Coordination Environment of Single‐Atom Catalysts for Enhanced Catalytic Performance in Hydrogen/Oxygen Evolution Reaction

Abstract

source could provide an auspicious alternative for reducing humanity's dependency on fossil fuels, thus lowering their environmental impact. [1][2][3][4][5] Electrochemical water splitting technology is intended for the large-scale production of high-purity H 2 . The primary reaction in the electrochemical water splitting cell is divided into two half-reactions: the oxygen evolution reaction (OER), which takes place in the anode, and the hydrogen evolution reaction (HER), which takes place in the cathode. The overall chemical reaction is simplified as H 2 O → H 2 (cathode) + ½ O 2 (anode), which can theoretically proceed with a minimum energy input of ΔG = 237.1 kJ mol −1 at a thermodynamic potential of 1.23 V. Nevertheless, the large overpotentials required to overcome the high activation barriers of the OER severely hinder the mass production of H 2 via electrochemical water splitting. [2,[6][7][8][9][10] In this regard, noble metalbased catalysts, such as IrO 2 /RuO 2 and Pt/C, possess great catalytic performances towards OER and HER, respectively. [11,12] The high costs and limited resources of noble metals have mandated researchers to seek alternatives in various affordable, non-noble metal-based electrocatalysts, like transition metal oxides (hydroxides), sulfides, phosphides, nitrides and carbides, and functional metal-free carbon composites. [13][14][15][16][17][18][19][20][21][22] However, these alternatives offer acceptable OER and HER catalytic performances when used in alkaline and acidic solutions, respectively, thereby limiting their practical applications. Besides, these materials are susceptible to rapid particle agglomeration during electrochemical operation, leading to limited atomic utilization efficiency. Noble metals like Pt, Pd, Ir, Rh, and Ru are still considered benchmark electrocatalytic materials for both HER and OER; hence, the development of cost-effective noble metal-based electrocatalysts is highly demanded.Previous studies pointed out that the catalytic activity of HER and OER catalysts is highly dependent on the density and chemical nature of the active sites, which can be improved via downscaling of the particle size. Single-atom catalysts (SACs) are the smallest possible size for a catalyst and could expose a larger surface area and tailor the atomic configuration and electronic structure, leading to optimal HER and OER activities. Thus, the development of SACs has become at the forefront of both Single-atom catalysts (SACs) hold the promise of utilizing 100% of the participating atoms in a reaction as active catalytic sites, achieving a remarkable boost in catalytic efficiency. Thus, they present great potential for noble metal-based electrochemical application systems, such as water electrolyzers and fuel cells. However, their practical applications are severely hindered by intrinsic complications, namely atom agglomeration and relocation, originating from the uncontrollably high surface energy of isolated singleatoms (SAs) during postsynthetic treatment processes or catalytic ...

Two-dimensional mineral hydrogel-derived single atoms-anchored heterostructures for ultrastable hydrogen evolution

“…5a clearly show that all of the interfacial models have higher Δ E H2O values than the single-phase models proving that the heterostructured interfaces effectively promote H 2 O adsorption. Moreover, the substantially different H 2 O adsorption abilities of monoatomic dispersed Fe atoms bonded with one (Fe@MoO 2 −1) or two (Fe@MoO 2 −2) O atoms in MoO 2 indicate that the local bonding environment of monoatomic dispersed Fe atoms greatly affects the H 2 O adsorption behaviour of electrocatalytic sites 40 – 42 . Furthermore, both the single-phase and heterostructured interfacial models show stronger H 2 O adsorption ability than Pt (111), demonstrating that MoP, MoP 2 , and MoO 2 nanocrystals and the heterostructured interfaces are critical for efficient H 2 O adsorption.…”

“…In order to build the MoP/MoP 2 , MoP/MoO 2 and MoP 2 /MoO 2 interfaces, the heterogeneous plane structure consisting of four layers of MoP 2 or MoO 2 with (2×2) supercells in the bottom, with the addition of MoP or MoP 2 clusters onto the top of them 54 . Since the DFT calculation results are very sensitive to the local coordination structure of the metallic centers 40 – 42 , a series of initial configurations with Fe atoms coordinating different number of O atoms are constructed to demonstrate the representative stable models with monoatomic dispersed Fe onto MoO 2 .Two different stable monoatomic dispersed Fe onto MoO 2 surface models (bonding with one or two O atoms, named Fe@MoO 2 −1 and Fe@MoO 2 −2 respectively) are obtained via a series of structure optimization test. The constructed initial configurations with Fe atoms coordinating more O atoms are unstable.…”

Element‐Doped Mxenes: Mechanism, Synthesis, and Applications

“…When the heteroatom is inserted into the original M n+1 X n T x layers by certain chemical methods, it will occupy the vacancy left by M or X atom, forming stable bonds to balance energy. [71,[76][77][78] Therefore, we summarize the research on the doping of various elements classified by transition metals, nonmetals, semiconductors, and rare earth elements. [79,80]…”

Theoretically revealing the activity origin of the hydrogen evolution reaction on carbon-based single-atom catalysts and finding ideal catalysts for water splitting

“…1,2 Thus, electrochemical water splitting has become a hot topic due to its ability to produce clean hydrogen without any carbon monoxide impurities and carbon emissions. 3–5 The main reactions in the electrochemical water-splitting cell involve the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), occurring at the anode and cathode, respectively. To date, expensive noble metals and their oxides ( e.g.…”

“…1,2 Thus, electrochemical water splitting has become a hot topic due to its ability to produce clean hydrogen without any carbon monoxide impurities and carbon emissions. [3][4][5] The main reactions in the electrochemical water-splitting cell involve the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), occurring at the anode and cathode, respectively. To date, expensive noble metals and their oxides (e.g., Pt and IrO 2 /RuO 2 ) [6][7][8] are still the most advanced catalysts for HER and OER, while the high cost and natural scarcity of noble metals hamper the practical application of the catalytic processes of OER and HER.…”