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Highlights: Oxygen-coordinated single-atom Mn catalyst was fabricated via introducing oxygen functional groups rich bacterial cellulose as the adsorption regulator through a combined impregnation–pyrolysis–etching synthetic route. Mn–O–C as the electrocatalyst exhibits superior electrocatalytic activity toward ammonia synthesis with a maximum NH3 yield rate of 1476.9 ± 62.6 μg h−1 cm−2 at − 0.7 V (vs. RHE) and a faradaic efficiency of 89.0 ± 3.8% at − 0.5 V (vs. RHE) under ambient conditions. Electrocatalytic mechanism of Mn–(O–C2)4 site for nitrate reduction reaction is unveiled by a combination of in situ spectroscopy characterization and computational study. Electrocatalytic nitrate reduction reaction has attracted increasing attention due to its goal of low carbon emission and environmental protection. Here, we report an efficient NitRR catalyst composed of single Mn sites with atomically dispersed oxygen (O) coordination on bacterial cellulose-converted graphitic carbon (Mn–O–C). Evidence of the atomically dispersed Mn–(O–C2)4 moieties embedding in the exposed basal plane of carbon surface is confirmed by X-ray absorption spectroscopy. As a result, the as-synthesized Mn–O–C catalyst exhibits superior NitRR activity with an NH3 yield rate (RNH3) of 1476.9 ± 62.6 μg h−1 cm−2 at − 0.7 V (vs. reversible hydrogen electrode, RHE) and a faradaic efficiency (FE) of 89.0 ± 3.8% at − 0.5 V (vs. RHE) under ambient conditions. Further, when evaluated with a practical flow cell, Mn–O–C shows a high RNH3 of 3706.7 ± 552.0 μg h−1 cm−2 at a current density of 100 mA cm−2, 2.5 times of that in the H cell. The in situ FT-IR and Raman spectroscopic studies combined with theoretical calculations indicate that the Mn–(O–C2)4 sites not only effectively inhibit the competitive hydrogen evolution reaction, but also greatly promote the adsorption and activation of nitrate (NO3−), thus boosting both the FE and selectivity of NH3 over Mn–(O–C2)4 sites. [ABSTRACT FROM AUTHOR]

Metal phthalocyanines (MPcs) have highly conjugated π electron systems and metal atoms acting as active centers, and so exhibit excellent electrocatalytic performance during the oxygen reduction reaction (ORR). However, these complexes also tend to undergo aggregation and exhibit poor electrical conductivity and minimal durability, all of which hinder their large‐scale industrial applications. In the present study, iron phthalocyanine (FePc) is applied to hollow carbon shells (HCSs) to generate an ORR catalyst containing single Fe atoms(HCS‐O‐FePc). The HCSs have numerous N/O‐based surface functional groups that promote the formation of Fe−O bonds with the FePc held in an axial coordination position. These axial Fe−O bonds disrupt the electron symmetry in the plane of the FePc molecules, which facilitate electron transfer. 1100HCS‐O‐FePc exhibits an onset potential of 0.98 V (vs RHE), a half‐wave potential of 0.91 V (vs RHE), an electron transfer number of 3.90, and durability better than that of a 20 % commercial Pt/C catalyst. Electrochemical impedance spectroscopy demonstrates that the ORR process over this material likely proceeds via a rapid 2+2 electron mechanism. This composite displays excellent oxygen reduction properties and is a promising alternative to Pt‐based ORR catalysts. [ABSTRACT FROM AUTHOR]

For electrocatalysts for the hydrogen evolution reaction (HER), encapsulating transition metal phosphides (TMPs) into nitrogen‐doped carbon materials has been known as an effective strategy to elevate the activity and stability. Yet still, it remains unclear how the TMPs work synergistically with the N‐doped support, and which N configuration (pyridinic N, pyrrolic N, or graphitic N) contributes predominantly to the synergy. Here we present a HER electrocatalyst (denoted as MoP@NCHSs) comprising MoP nanoparticles encapsulated in N‐doped carbon hollow spheres, which displays excellent activity and stability for HER in alkaline media. Results of experimental investigations and theoretical calculations indicate that the synergy between MoP and the pyridinic N can most effectively promote the HER in alkaline media. [ABSTRACT FROM AUTHOR]

Given the efficiency, stability and sustainability, the carbon-based materials have become one of promising bifunctional electrocatalysts to the electrochemical water splitting, involving hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, there are still many challenges about the design and mechanism study of the carbon-based electrocatalysts. In this paper, we reported B, N co-doping carbon nanosheets which were synthesized via cationic intercalation stripping guar gum carbon aerogels pre-crosslinked by borate, B(OH) 4 -. This facile strategy not only realizes the structure tailoring, but also concurrently improves the doping efficiency and the stability of the hetero atoms. Specifically, the cost-efficient carbon-based bifunctional catalyst (B5/GCS) shows an outstanding HER and OER performance displaying a remarkable activity both in acidic and alkaline media, low onset potentials for both HER (39.12 mV) and OER (1.38 V) in the same electrolyte (0.5 M H 2 SO 4). Notably, when employed as the bifunctional electrocatalysts with a two-electrode electrolyzer for water splitting, the B5/GCS generated a cell voltage of 1.45 V to attain 10 mA cm−2 in 0.5 M H 2 SO 4. Furthermore, a series of experiments combining density functional theory calculations revealed that the observed superb water splitting activity could be attributed to a synergistic effect of N, B co-doping and the formation of fragmented nanosheets with topological defects, which collaboratively promotes the proton adsorption and catalytic kinetics. A advanced carbon-based bifunctional catalyst are designed and fabricated by a facile two-step strategy - borate chemical crosslinking guar gum gel and subsequent cationic intercalation stripping, as water splitting catalyst, the optimal B5/GCS exhibits extraordinary HER and OER performance – on par with the benchmark noble metal catalyst. Image 1 [ABSTRACT FROM AUTHOR]

[Display omitted] • Three-dimensional ordered macroporous frameworks with NiN 4 sites were obtained. • 3DOM Ni N C was highly efficiency for ORR and OER performances in neutral condition. • The neutral zinc-air batteries exhibited outstanding long term stability of 580 cycles at 1.0 mA cm−2. • The failure mechanism of air electrode in neutral condition was revealed. Neutral zinc-air batteries prevent the carbon based catalysts from being oxidized during cycling, which show excellent potential for long-term energy storage. Three-dimensional ordered macroporous nitrogen doped carbon frameworks with NiN 4 (3DOM Ni N C) were constructed by in situ reaction of Ni nanoparticles and dicyandiamide. The 3DOM Ni N C bifunctional catalysts exhibit comparable oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) efficiency and stablity. The 3D interconnected structure of 3DOM Ni N C provides sufficient channel for mass transfer, resulting in high power density (35 mW cm−2) and long cycle life (580 cycles) of neutral zinc-air batteries. Meanwhile the failure mechanism in neutral electrolyte was discussed. [ABSTRACT FROM AUTHOR]