Single-atom catalysts based on metal−N 4 moieties and anchored on carbon supports (defined as M−N−C) are promising for oxygen reduction reaction (ORR). Among those, M−N−C catalysts with 4d and 5d transition metal (TM 4d,5d ) centers are much more durable and not susceptible to the undesirable Fenton reaction, especially compared with 3d transition metal based ones. However, the ORR activity of these TM 4d,5d −N− C catalysts is still far from satisfactory; thus far, there are few discussions about how to accurately tune the ligand fields of singleatom TM 4d,5d sites in order to improve their catalytic properties. Herein, we leverage single-atom Ru−N−C as a model system and report an S-anion coordination strategy to modulate the catalyst's structure and ORR performance. The S anions are identified to bond with N atoms in the second coordination shell of Ru centers, which allows us to manipulate the electronic configuration of central Ru sites. The S-anion-coordinated Ru−N−C catalyst delivers not only promising ORR activity but also outstanding longterm durability, superior to those of commercial Pt/C and most of the near-term single-atom catalysts. DFT calculations reveal that the high ORR activity is attributed to the lower adsorption energy of ORR intermediates at Ru sites. Metal−air batteries using this catalyst in the cathode side also exhibit fast kinetics and excellent stability.

Developing low-cost, high performance, stable non-noble bifunctional electrocatalysts for overall water splitting is of great importance for future energy supplement. Despite recent advances in the synthesis of transition metal selenide nanostructures, the fabrication of porous nanosheet based binder-free electrode with more active sites remains a major challenge. Herein, the self-templating construction of a porous CoSe2 nanosheet array on carbon cloth (p-CoSe2/CC) has been reported by vapor selenizing the preprepared α-Co­(OH)2 nanosheet array precursor. Arising from large active surface area, fast diffusion of generated gas and strong structural stability, the as-obtained p-CoSe2/CC can serve as an efficient bifunctional electrocatalyst for both OER and HER in alkaline electrolyte, with a current density of 10 mA cm–2 at overpotential of 243 mV for OER and 138 mV for HER, respectively. Moreover, when p-CoSe2/CC is assembled as an alkaline electrolyzor, it only needs a cell voltage of 1.62 V at 10 mA cm–2 and shows excellent long-term stability of 20 h. The versatile fabrication strategy with self-templated porous structure proves a new way to construct other advanced metal selenide for energy conversion and storage.

The exploration of indurative and stable low-cost catalysts for hydrogen evolution reaction (HER) is of great importance for hydrogen energy economy, but it still faces challenges. Herein, we report a Cl-doped Ni 3 S 2 (Cl−Ni 3 S 2 ) nanoplate catalyst vertically grown on Ni foam with outstanding activity and durability for HER, which only requires an overpotential of 67 mV to reach a current density of 10 mA cm −2 in alkaline media and exhibits negligible degradation after 30 h of operation. Both the advanced X-ray absorption fine structure (XAFS) and density functional theory (DFT) calculation validate that Cl doping can optimize the electronic structure and the intrinsic activity of Ni 3 S 2 . This study devoted to the revelation of the impact of ionic doping on the activity of catalysts at the atomic scale can provide the direction for the rational design of novel and advanced HER electrocatalysts.

Exploiting active and stable non‐precious metal electrocatalysts for alkaline hydrogen evolution reaction (HER) at large current density plays a key role in realizing large‐scale industrial hydrogen generation. Herein, a self‐supported microporous Ni(OH)x/Ni3S2 heterostructure electrocatalyst on nickel foam (Ni(OH)x/Ni3S2/NF) that possesses super‐hydrophilic property through an electrochemical process is rationally designed and fabricated. Benefiting from the super‐hydrophilic property, microporous feature, and self‐supported structure, the electrocatalyst exhibits an exceptional HER performance at large current density in 1.0 M KOH, only requiring low overpotential of 126, 193, and 238 mV to reach a current density of 100, 500, and 1000 mA cm−2, respectively, and displaying a long‐term durability up to 1000 h, which is among the state‐of‐the‐art non‐precious metal electrocatalysts. Combining hard X‐rays absorption spectroscopy and first‐principles calculation, it also reveals that the strong electronic coupling at the interface of the heterostructure facilitates the dissociation of H2O molecular, accelerating the HER kinetics in alkaline electrolyte. This work sheds a light on developing advanced non‐precious metal electrocatalysts for industrial hydrogen production by means of constructing a super‐hydrophilic microporous heterostructure.

Atomically dispersed 3D transitional metal active sites with nitrogen coordination anchored on carbon support have emerged as a kind of promising electrocatalyst toward oxygen reduction reaction (ORR) in the field of fuel cells and metal-air cells. However, it is still a challenge to accurately modulate the coordination structure of single-atom metal sites, especially first-shell coordination, as well as identify the relationship between the geometric/electronic structure and ORR performance. Herein, a carbon-supported singleatom nickel catalyst is fabricated with boron and nitrogen dual coordination (denoted as Ni-B/N-C). The hard X-ray absorption spectrum result reveals that atomically dispersed Ni active sites are coordinated with one B atom and three N atoms in the first shell (denoted as Ni-B 1 N 3 ). The Ni-B/N-C catalyst exhibits a half-wave potential (E 1/2 ) of 0.87 V versus RHE, along with a distinguished long-term durability in alkaline media, which is superior to commercial Pt/C. Density functional theory calculations indicate that the Ni-B 1 N 3 active sites are more favorable for the adsorption of ORR intermediates relative to Ni-N 4 , leading to the reduction of thermodynamic barrier and the acceleration of reaction kinetics, which accounts for the increased intrinsic activity.

Designing dual-metal atoms efficient bifunctional oxygen electrocatalyst by a one-step adsorption and a pyrolysis steps.

studied, but their low abundance and high price hinder the larger scale application. [3,4] Thus, it is highly desirable to explore affordable and efficient Pt-free ORR catalysts. [5] Atomically dispersed 3d transition metal with nitrogen ligand anchored on carbon (M-NC), such as Fe-NC or Co-NC et al., are regarded as the most promising Pt-free catalysts because of their inspiring ORR activities, welldefined structure and low cost. [6,7] Recent studies demonstrated that the planar M-N 4 moiety is the real active sites toward ORR, which could directly adsorb O 2 molecular and efficiently break OO bond, therefore facilitating ORR kinetics. [8,9] However, despite great progress in boosting the activities of Fe-NC and Co-NC catalysts, the long-term durability of the catalysts is far from satisfactory, which inhabits their further application. [10][11][12] The dissolution of metals and the corrosion of carbon support are responsible for the degradation of the catalytic activities for M-NC catalysts, which is mainly attributed to the oxidation attack of the by-product of hydrogen peroxide (H 2 O 2 ) and hydroxyl radical (OH•) generated by Fenton reaction (Fe 2+ + H 2 O 2 →Fe 3+ + OH − + OH•), especially for the advanced Fe-NC and Co-NC catalysts. [11,13,14] Thereby, developing M-NC catalysts that could avoid the generation of H 2 O 2 and OH• is an important research direction. [15] For instance, Mn-NC and Ni-NC catalysts have been reported as durable ORR catalysts due to the high selectivity of 4e − reaction transfer and the weak Fenton reaction between H 2 O 2 and Mn/Ni ions. [16] Compared with Mn-NC catalyst that is difficult to synthesize due to multivalence Mn ions (from 0 to +7), [17] the single-atom Ni-NC is easier to fabricate. However, on account of the relatively weak adsorption strength of the ORR intermediates on Ni-N 4 sites, the Ni-NC catalyst displays unsatisfactory activities. [18,19] Hence, further optimizing the electronic structure of the active Ni site is highly desirable.Altering ligand fields in single-atom metal center through anion (S, P et al.) modulation has been demonstrated as an efficient strategy to regulate the electronic structure of the active metal centers. [20,21] Conventionally, the introduced anions are located at the second-shell or higher shell of metal center, which could change the electronic densities of active M-N 4 sites through the withdrawing/donating effects, thereby boosting their intrinsic activities. [22] But the indirect interaction between Atomically dispersed nitrogen-coordinated 3d transition-metal site on carbon support (M-NC) are promising alternatives to Pt group metal-based catalysts toward oxygen reduction reaction (ORR). However, despite the excellent activities of most of M-NC catalysts, such as Fe-NC, Co-NC et al., their durability is far from satisfactory due to Fenton reaction. Herein, this work reports a novel Si-doped Ni-NC catalyst (Ni-SiNC) that possesses high activity and excellent stability. X-ray absorption fine structure and aberrationcorrected tran...

Developing ultrahigh-activity and ultralong-durability electrocatalysts for oxygen evolution reaction (OER) in alkaline media is of great significance for large-scale alkaline water splitting. Herein, we report a self-supported heterostructure electrocatalyst composed of Ni 3 S 2 nanosheet arrays decorated with Ag nanoparticles grown on nickel foam (Ag/Ni 3 S 2 /NF). Specifically, the insightful studies reveal that the amorphous NiOOH in situ formed on the surface of heterostructure electrocatalyst during OER (NiOOH@Ag/Ni 3 S 2 /NF) is regarded as the real active species. This self-constructed electrode only needs low overpotentials of 183, 195, and 263 mV at the current density of 10, 20, and 100 mA cm −2 , respectively, as well as a low Tafel slope of 37 mV dec −1 in 1 M KOH, and is maintained for 500 h almost without any degradation at a high current density of 100 mA cm −2 . Density functional theory (DFT) calculations reveal that the synergistic effects among multiple components can effectively boost the intrinsic OER activity via increasing conductivity and optimizing binding energy of oxygen-contained intermediates, and the enhanced Ni−O bonding accounts for the superior durability. This work provides deep insight into the key role of Ag on boosting both the catalytic activity and the stability of nickel sulfides toward OER.