An Amorphization-Engineered Catalyst for Electrocatalytic Reduction of Nitric Oxide to Ammonia.

Electrocatalytic NO-to-NH3 conversion (NORR) provides a fascinating route toward the eco-friendly and valuable production of NH3. In this study, amorphous FeS2 (a-FeS2) is first demonstrated as a high-efficiency catalyst for the NORR, showing a maximum FENH3 of 92.5% with a corresponding NH3 yield rate of 227.1 µmol h-1 cm-2, outperforming most NORR catalysts reported earlier. Experimental measurements combined with theoretical computations clarify that the exceptional NORR activity of a-FeS2 originates from the amorphization-induced upshift of the d-band center to promote the NO activation and NO-to-NH3 hydrogenation energetics.

Vanadium Diboride (VB2) for NO Electroreduction to NH3.

We report VB2 as an efficient electrocatalyst for NO-to-NH3 electroreduction (NORR), showing the highest NH3-Faradaic efficiency of 89.6% with the corresponding NH3 yield rate of 198.3 µmol h-1 cm-2 at -0.5 V vs RHE. Theoretical calculations demonstrate that B sites of VB2 act as the key active centers which can facilitate the NORR protonation energetics and inhibit the competitive hydrogen evolution, boosting both NORR activity and selectivity.

Iron Diboride (FeB2) for the Electroreduction of NO to NH3.

We report iron diboride (FeB2) as a high-performance metal diboride catalyst for electrochemical NO-to-NH3 reduction (NORR), which shows a maximum NH3 yield rate of 289.3 µmol h-1 cm-2 and a NH3-Faradaic efficiency of 93.8% at -0.4 V versus reversible hydrogen electrode. Theoretical computations reveal that Fe and B sites synergetically activate the NO molecule, while the protonation of NO is energetically more favorable on B sites. Meanwhile, both Fe and B sites preferentially absorb NO over H atoms to suppress the competing hydrogen evolution.

Tandem Electrocatalytic Nitrate Reduction to Ammonia on MBenes.

We demonstrate the great feasibility of MBenes as a new class of tandem catalysts for electrocatalytic nitrate reduction to ammonia (NO3 RR). As a proof of concept, FeB2 is first employed as a model MBene catalyst for the NO3 RR, showing a maximum NH3 -Faradaic efficiency of 96.8 % with a corresponding NH3 yield of 25.5 mg h-1 cm-2 at -0.6 V vs. RHE. Mechanistic studies reveal that the exceptional NO3 RR activity of FeB2 arises from the tandem catalysis mechanism, that is, B sites activate NO3 - to form intermediates, while Fe sites dissociate H2 O and increase *H supply on B sites to promote the intermediate hydrogenation and enhance the NO3 - -to-NH3 conversion.

A metal-free catalyst for electrocatalytic NO reduction to NH3.

Metal-free boron phosphide (BP) is explored for the first time as an effective catalyst for electrocatalytic NO reduction to NH3, showing a high NH3-faradaic efficiency of 83.3% with an NH3 yield rate of 96.6 µmol h-1 cm-2, surpassing most metal-based catalysts. Theoretical results reveal that the B and P atoms of BP can serve as dual-active centers to synergistically activate NO, promote the NORR hydrogenation process and inhibit the competing hydrogen evolution reaction.

Boron phosphide as an efficient metal-free catalyst for nitrate electroreduction to ammonia.

Boron phosphide (BP) is first explored as an efficient metal-free catalyst towards the NO3RR, delivering the highest NH3-faradaic efficiency of 96.3% with a corresponding NH3 yield rate of 3.1 mg h-1 cm-2, outperforming most reported metal-based NO3RR catalysts. Theoretical calculations unravel that active B centers not only enable the efficient NO3- activation and hydrogenation with a low energy barrier, but also preferentially absorb NO3- over H adatoms to prohibit the competing hydrogen evolution, enhancing both NO3RR activity and selectivity.

Atomically Mo-Doped SnO2-x for efficient nitrate electroreduction to ammonia.

Electrochemical NO3--to-NH3 reduction (NO3RR) emerges as an appealing strategy to alleviate contaminated NO3- and generate valuable NH3 simultaneously. However, substantial research efforts are still needed to advance the development of efficient NO3RR catalysts. Herein, atomically Mo-doped SnO2-x with enriched O-vacancies (Mo-SnO2-x) is reported as a high-efficiency NO3RR catalyst, delivering the highest NH3-Faradaic efficiency of 95.5% with a corresponding NH3 yield rate of 5.3 mg h-1 cm-2 at -0.7 V (RHE). Experimental and theoretical investigations reveal that d-p coupled Mo-Sn pairs constructed on Mo-SnO2-x can synergistically enhance the electron transfer efficiency, activate the NO3- and reduce the protonation barrier of rate-determining step (*NO→*NOH), thereby drastically boosting the NO3RR kinetics and energetics.

Ampere-Level Nitrate Electroreduction to Ammonia over Monodispersed Bi-Doped FeS2.

Electrochemical conversion of NO3- into NH3 (NO3RR) holds an enormous prospect to simultaneously yield valuable NH3 and alleviate NO3- pollution. Herein, we report monodispersed Bi-doped FeS2 (Bi-FeS2) as a highly effective NO3RR catalyst. Atomic coordination characterizations of Bi-FeS2 disclose that the isolated Bi dopant coordinates with its adjacent Fe atom to create the unconventional p-d hybridized Bi-Fe dinuclear sites. Operando spectroscopic measurements combined with theoretical calculations disclose that Bi-Fe dinuclear sites can synergistically enhance the hydrogenation energetics of NO3--to-NH3 pathway, while suppressing the competitive hydrogen evolution, leading to a high NO3RR selectivity and activity. Consequently, the specially designed flow cell equipped with Bi-FeS2 exhibits a high NH3 yield rate of 83.7 mg h-1 cm-2 with a near-100% NO3--to-NH3 Faradaic efficiency at an ampere-level current density of 1023.2 mA cm-2, together with an excellent long-term stability for 100 h of electrolysis, ranking almost the highest performance among all reported NO3RR catalysts.

FeS2 nanoparticles on reduced graphene oxide: an efficient electrocatalyst for nitrate electroreduction to ammonia.

Electrocatalytic nitrate-to-ammonia conversion (NO3RR) represents a promising approach for achieving both sustainable NH3 synthesis and wastewater treatment. Herein, we first demonstrate the great feasibility of using pyrite FeS2 as an effective and durable NO3RR catalyst. The developed FeS2 nanoparticles supported on reduced graphene oxide (FeS2/RGO) deliver the maximum NH3-Faradaic efficiency of 83.7% with a corresponding NH3 yield of 2.32 mg h-1 cm-2 at -0.6 V (RHE). FeS2/RGO also exhibits excellent stability during the cycling and long-term electrolysis tests. DFT calculations reveal that NO3- can be efficiently activated on surface Fe sites, which can drive the NO3RR process through an NHO pathway with a low energy barrier.