Search

The development of stable, low-cost, and highly efficient electrocatalysts for the N2 reduction reaction (NRR) process is challenging but crucial for ammonia production. Herein, we demonstrate the synthesis of pyrite nanoparticles wrapped by graphene oxide (FeS2@GO) acting as a highly efficient NRR catalyst in a wide pH range. The FeS2 nanoparticles are uniformly dispersed across the GO nanosheet, thus leading to the fine exposure of active sites, the promotion of charge transfer, and the increment of a contact surface area, which are all beneficial for a desired catalyst. In the meantime, the low-coordinated Fe atoms are activated as highly active sites, which is in favor of the enhanced electrochemical performance for the NRR. Furthermore, density functional theory (DFT) calculations illustrated that the high activity of N2 reduction over the FeS2@GO catalyst arises from the well-exposed Fe active sites and the increment of charge density at the valence band edge. Benefiting from the well-optimized interface, the barrier of the addition of the first hydrogen atom to N2 forming *NNH species as the potential-determining step is as low as 0.93 eV in N2 electroreduction. The electrochemical test results reveal that, as expected, FeS2@GO exhibits high Faradaic efficiencies (4.7% in 0.1 M HCl solution and 6.8% in 0.1 M Na2SO4 solution) and advanced NH3 yields (78.6 and 27.9 μg h-1 mgcat.-1 in 0.1 M HCl and 0.1 M Na2SO4 solutions, respectively) in both acid and neutral conditions. This work offers a new avenue for exploring novel electrocatalysts, which has great promise to accelerate the practical application of the NRR.

In comparison with the traditional Haber–Bosch process, the electrocatalytic nitrogen reduction reaction (NRR) with high purity and sustainability became a popular process to satisfy the demand of ammonia. However, the strong competing reaction (hydrogen evolution reaction, HER) and low reaction efficiency hinder the practical applications of NRR. Thus, the development of advanced NRR catalysts by regulating the electronic structure and the activity of single active sites is urgent. Here, in our study, vanadium-doped NiS2 (V–NiS2) nanospheres with abundant active sites were first proposed in the NRR field, which exhibited excellent catalytic activity with a high NH3 yield (47.63 μg h−1 mg−1cat., at −0.45 V) and good faradaic efficiency (FE) (9.37% at −0.35 V) in a 0.1 M HCl solution. Moreover, V–NiS2 also performed desired selectivity and stability. This study provides a pathway to design advanced NRR catalysts for practical applications.

The development of earth-abundant and high-efficiency electrocatalysts for overall water splitting is highly fascinating and still presents a challenge caused by the low activity for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) at the same time. In this paper, active cobalt-doped pyrite nanospheres with a porous structure are fabricated for the first time as advanced catalysts for water splitting in an alkaline solution. With the incorporation of cobalt atoms, the electronic structure of pyrite is well-tuned, with high conductivity as well as more active sites being obtained, which finally results in a superior bifunctional water splitting performance. Only 1.60 V is required to reach the current density of 10 mA cm−2, which is smaller than that of other transition metal sulfides.

The development of effective non-noble metal based catalysts for the electrocatalytic oxygen evolution reaction (OER) at lower overpotentials has attracted tremendous attention due to its important role for various electrochemical energy storage and conversion devices. Transition metal based oxides have been deeply investigated, benefiting from their promising catalytic activity as well as their low cost. However, among these oxides, the OER efficiency of molybdenum oxides has rarely been studied due to its limited intrinsic activity. Herein, we reported amorphous cobalt-doped molybdenum oxide (Co–MoOx) with a core–shell structure as an effective OER catalyst for the first time. Benefiting from the cobalt doping as well as the amorphous structural character, the charge transfer process and the active sites are both well optimized, which is highly desired for an advanced electrocatalyst. As expected, the Co–MoOx catalyst afforded an extremely low overpotential of 340 mV at a current density of 10 mA cm−2, and a small Tafel slope of 49 mV dec−1 in KOH solution. This work shows an effective strategy for the realization of highly efficient OER electrocatalysts.

Transition metal oxides have attracted tremendous attention as active and stable electrocatalysts for hydrogen or oxygen evolution from water splitting. However, their application as bifunctional catalysts for overall water splitting is still hindered by their limited activity. In this paper, via the surface defect engineering strategy, a bifunctional electrocatalyst based on oxygen vacancy enriched CoFe2O4 (r-CFO) nanosheets was successfully fabricated, exhibiting desired overall water splitting activity. DFT calculations demonstrated that benefitting from the incorporation of oxygen vacancies, the adsorption energy (Eads) of H2O and the Gibbs free energy change for hydrogen adsorption (ΔGH*) are both well optimized, leading to the fine modulation of active site activity. Meanwhile, along with oxygen vacancy doping, the density of states across the Fermi level increased as well, which would be conducive to fast electron transportation. As expected, the r-CFO catalyst afforded obviously lower overpotentials of 280 mV and 121 mV to achieve a current density of 10 mA cm−2 for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. Furthermore, r-CFO exhibited excellent overall water splitting activity with a voltage of 1.53 V to reach a current density of 10 mA cm−2. This work highlights the vital role of surface defect engineering based on transition metal oxides toward advanced electrocatalysts.

The development of active and inexpensive electrocatalysts for the oxygen evolution reaction (OER) to promote water splitting has always been a major challenge. Cobalt-based oxides and sulfides have been actively investigated due to their low cost and high activity. However, the lower intrinsic conductivity of cobalt oxide and the inferior stability of cobalt sulfides still limit their practical application. Herein, CoO was chosen for a proof-of-concept study in which the anion-doping strategy was used to obtain an excellent catalyst. Sulfur incorporation optimizes the charge-transfer properties and active sites of sulfur-doped CoO (S-CoO) and thus gives rise to improved catalytic activity. Besides sulfur doping, the stable framework of the cobalt oxide was well maintained, and thus high stability of S-CoO throughout the reaction process was ensured.

Developing efficient and non-noble metal electrocatalysts for oxygen evolution reaction (OER) at lower overpotential has been considered as a clean and effective strategy for replacing fossil feedstocks. Transitional metal oxides (TMO) electrocatalysts have been actively pursued because of their low-cost and strong stability in alkaline. However, the efficiency for most of developed TMO has been refrained by poor intrinsic electrical conductivity and exposed active sites. Herein, we demonstrate a sulfur incorporation strategy to accomplish greatly optimized OER performance in CoFe 2 O 4 /MWCNT (S-CFO/MWCNT) nanocomposite. Sulfur incorporation into CoFe 2 O 4 not only brings about more active sites in CFO frameworks, but also retains the pristine stable inverse spinel crystal structure which renders the high durability of the S-CFO/MWCNT catalyst. Specifically, the electrocatalysts exhibited greatly optimized OER catalytic activity with overpotential of about 0.36 V achieving current density of about 10 mA cm −2 and Tafel slope of about 43 mV dec −1 , together with stronger stability. Our work demonstrates an effective way to pursue highly efficient OER electrocatalysts.

Exploring highly efficient and low cost bifunctional electrocatalysts for overall water splitting is of primary importance for renewable energy storage. Here, a novel amorphous CoFeOx(OH)y/CoOx(OH)y nanosphere (CFOH/COH) with unique core/shell structure was produced through a simple one-step solvothermal reaction, which exhibited enhanced activity for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) across the water splitting process. Benefited from the unique core/shell character, the amorphous structure as well as the amorphous interface, the active sites of CFOH/COH were well optimized, thus finally leading to the activity enhancement. The CFOH/COH-1 catalyst (with the Co/Fe ratio of about 1) displayed the best performance among the tested catalysts, exhibiting the overpotentials of 0.324 V and 0.263 V to achieve the current density of 10 mA cm−2 for OER and HER in 1.0 M KOH solution, respectively, smaller than those of pure Fe- or Co-based amorphous catalysts. Furthermore, the CFOH/COH-1 exhibited robust catalytic activity with a voltage of 1.59 V to reach a current density of 10 mA cm−2, when adopted as the bifunctional catalyst for full water splitting. This work highlights the important role of amorphous transition metal based heterostructure for boosting the HER and OER performance.

Electrocatalytic nitrogen reduction reaction (NRR) to produce ammonia as a promising technology for alternative Haber-Bosch process attracted vast attention. Unfortunately, the absorption of N2 and the breaking of stable triple bond still handicap the practical application of NRR. Here in our work, the Fe-doped Ni2P was fabricated and adopted as the advanced catalyst for NRR firstly. Benefited from the porous nanosheets structure, both the active sites and the surface area were increased. Meanwhile, along with the iron doping, the active centers on Ni site were activated and the new active centers on Fe site were created, thus promoting the adsorption of N2 and the weakening of N N bonds. Specifically, the Fe-Ni2P exhibited excellent activity, with NH3 yield of 88.51 μg h−1 mg−1cat. and FE of 7.92% being obtained at -0.3 V (vs. RHE), highlighting the heteroatom doping strategy as a novel guidance to the design of advanced NRR catalyst.