Product selectivity in multielectron electrocatalytic reactions is crucial to energy conversion efficiency and chemical production. However, a present practical drawback is the limited understanding of actual catalytic active sites. Here, using as a prototype single-atom catalysts (SACs) in acidic oxygen reduction reaction (ORR), we report the structure–property relationship of catalysts and show for the first time that molecular-level local structure, including first and second coordination spheres (CSs), rather than individual active atoms, synergistically determines the electrocatalytic response. ORR selectivity on Co-SACs can be tailored from a four-electron to a two-electron pathway by modifying first (N or/and O coordination) and second (C–O–C groups) CSs. Using combined theoretical predictions and experiments, including X-ray absorption fine structure analyses and in situ infrared spectroscopy, we confirm that the unique selectivity change originates from the structure-dependent shift of active sites from the center Co atom to the O-adjacent C atom. We show this optimizes the electronic structure and *OOH adsorption behavior on active sites to give the present “best” activity and selectivity of >95% for acidic H2O2 electrosynthesis.

Electrochemical fixation of N2 to ammonia is a promising strategy to store renewable energy and mitigate greenhouse gas emissions. However, it usually suffers from extremely low ammonia yield and Faradaic efficiency because of the lack of efficient electrocatalysts and the competing hydrogen evolution reaction. Herein, we report that the semiconducting bismuth can be a promising catalyst for ambient electrocatalytic N2 reduction reaction (NRR). A two-dimensional mosaic bismuth nanosheet (Bi NS) was fabricated via an in situ electrochemical reduction process and exhibited favorable average ammonia yield and Faradaic efficiency as high as 2.54 ± 0.16 μgNH3 cm–2 h–1 (∼13.23 μg mgcat. –1 h–1) and 10.46 ± 1.45% at −0.8 V versus reversible hydrogen electrode in 0.1 M Na2SO4. The high NRR electrocatalytic activity of the Bi NS could be attributed to the sufficient exposure of edge sites coupled with effective p-orbital electron delocalization in the mosaic bismuth nanosheets. In addition, the semiconducting feature, which limits surface electron accessibility, could effectively enhance the Faradaic efficiency. This work highlights the potential importance of less reactive main group elements with tunable p-electron density, semiconducting property, and ingenious nanostructure for further exploration of N2 reduction reaction electrocatalysts.

also aggravate the greenhouse effect. [8] Considering the huge energy consumption of this process and the great potential of NH 3 in future energy systems, protonassisted electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions is becoming increasingly important in realizing low-cost artificial nitrogen fixation. [10][11][12] More importantly, the NRR system can be easily integrated with renewable solar and wind energy into an environmentally benign process for NH 3 production. [2,7] Even though various materials have shown NRR activity in aqueous system, their performance are still hindered by the sluggish reaction kinetics and competitive hydrogen evolution reaction (HER) resulting in poor activity and unsatisfactory selectivity. [13][14][15] The active site for electrochemical NRR needs twofold properties: for one thing, it can accept the lone-pair electrons for effective N 2 adsorption and for the other thing it can donate electrons to antibonding orbitals of dinitrogen molecules for the NN triple-bond activation. [9,13,[16][17][18][19][20] From this perspective, vacancy-engineering materials are ideal for practical applications. [9,16,20] By virtue of the electron redistribution and special chemical properties, the vacancies can provide unique active sites for nitrogen adsorption and activation. [9,[21][22][23][24] Up to now, the most common vacancy that has been studied for NRR is oxygen vacancy. For example, oxygen vacancies on transition metal oxides are active for NRR by enhancing the dinitrogen molecule adsorption. [9,25] However, oxygen vacancy can also improve the HER performance of the host matrix, which may result in poor NRR selectivity. [26][27][28] Alternatively, nitrogen vacancies on transition metal nitride (TMN) are considered as an ideal active site for NRR because of its unique vacancy properties for dinitrogen molecule adsorption and poor HER activity. [29,30] However, the nitrogen vacancy on TMN would be deactivated during NRR process thus results in poor stability. [29] In addition, researchers claim that some TMNs are inactive toward NRR in aqueous system, which is in contrary to theoretical calculations. [31] To gain insightful understanding of NRR mechanism, it is necessary to design TMNs with simplex structure and stable surface vacancies for the linkage of theoretical models and real-world catalysts. 2D material has onefold and fully exposed crystal surface, which is widely used as platform for both theoretical calculations and Electrochemical nitrogen reduction reaction (NRR) under ambient conditions provides an avenue to produce carbon-free hydrogen carriers. However, the selectivity and activity of NRR are still hindered by the sluggish reaction kinetics. Nitrogen Vacancies on transition metal nitrides are considered as one of the most ideal active sites for NRR by virtue of their unique vacancy properties such as appropriate adsorption energy to dinitrogen molecule. However, their catalytic performance is usually limited by the unstable feature. Herein, a new ...

The electrochemical reduction of O2 via a two‐electron reaction pathway to H2O2 provides a possibility for replacing the current anthraquinone process, enabling sustainable and decentralized H2O2 production. Here, a nitrogen‐rich few‐layered graphene (N‐FLG) with a tunable nitrogen configuration is developed for electrochemical H2O2 generation. A positive correlation between the content of pyrrolic‐N and the H2O2 selectivity is experimentally observed. The critical role of pyrrolic‐N is elucidated by the variable intermediate adsorption profiles as well as the dependent negative shifts of the pyrrolic‐N peak on X‐ray adsorption near edge structure spectra. By virtue of the optimized N doping configuration and the unique porous structure, the as‐fabricated N‐FLG electrocatalyst exhibits high selectivity toward electrochemical H2O2 synthesis as well as superior long‐term stability. To achieve high‐value products on both the anode and cathode with optimized energy efficiency, a practical device coupling electrochemical H2O2 generation and furfural oxidation is assembled, simultaneously enabling a high yield rate of H2O2 at the cathode (9.66 mol h−1 gcat−1) and 2‐furoic acid at the anode (2.076 mol m−2 h−1) under a small cell voltage of 1.8 V.

Developing efficient and low-cost electrocatalysts for the hydrogen evolution reaction (HER) is important for clean energy systems. Non-noble transition metals are the most promising candidates for replacement of conventional Pt group catalysts for the HER. However, most non-noble metals show poor HER activity due to their intrinsic electronic structures. Herein, we use a multifaceted heteroatom doping method (nitrogen, sulfur, and phosphorus) to directly and continuously fine-tune the electronic structure and HER activity of non-noble metals without changing their chemical composition. As a proof-of-concept, a nitrogen and phosphorus dual-doped Ni catalyst is explored by precisely manipulating doping modes, revealing the best HER performance among all doped Ni catalysts tested. The doping-induced charge redistribution in the Ni metal significantly influences its catalytic performance for the HER in alkaline media, which is confirmed by merging theoretical calculation with synchrotron-based spectroscopy. The principle that can bridge the doping modes and HER activity of the doped catalysts is built with a volcano relationship.

This is because chlorine evolution takes place at the counter electrode and highly corrosive hypochlorite by-products block the active sites of the noble metal catalysts. [6,13,18] Consequently, development of stable and active electrocatalysts for seawater splitting is of crucial importance for this process. Transition metal nitrides (TMNs) have excellent electrical conductivity and corrosion resistance and have demonstrated good stability for seawater splitting. [18-20] However, most of the bulk TMNs reported exhibit unsatisfactory HER activity due to a suboptimal hydrogen bonding energy. [21,22] Consequently, material optimization strategies, such as vacancy engineering, alloying, interface engineering, and heteroatom doping are usually needed to improve their activity. [23-28] For example, interfacing MoN with C 3 N 4 can greatly promote HER activity in alkaline media. [29] Tungsten and phosphorus doping in Co 3 N can manipulate the dehydrogenation kinetics and increase hydrogen production. [27] Despite significant investigation into TMNs, adequate activity and corrosion resistance are still required to be achieved simultaneously, and more advanced modification methods need to be developed. Manipulating the stoichiometry is one such way to optimize the properties of TMNs. Using this strategy, the N atom ratio in the metal matrix can be tuned to regulate the TMN electronic structure. [18,24,25,30] The two main approaches to controlling the nitrogen content in TMNs are the nitrogen-rich process and the incomplete nitridation process. [31-33] The nitrogen-rich process aims to embed extra nitrogen atoms into the TMN lattice but usually requires high-temperature and high-pressure conditions due to sluggish thermodynamics. [30,31,34,35] The incomplete nitridation process can limit the metal-nitrogen bonding in the matrix and promote the formation of metal/ metal nitride interfaces, which generally offers better conductivity and subsequent electrocatalytic activity. [23,25,33,36] However, the stoichiometry in a metal/metal nitride heterostructure is difficult to control and deficient or superfluous nitridation can lead to poor electrocatalytic activity. Herein, we synthesized a nickel surface nitride encapsulated in a carbon shell (Ni-SN@C) using an unsaturated nitriding process. Compared to conventional TMNs or metal/metal nitride heterostructures, the unsaturated Ni-SN@C has no detectable bulk nickel nitride phase. Instead, the main chemical composition of Ni-SN@C is metallic Ni but with unique Electrocatalytic production of hydrogen from seawater provides a route to low-cost and clean energy conversion. However, the hydrogen evolution reaction (HER) using seawater is greatly hindered by the lack of active and stable catalysts. Herein, an unsaturated nickel surface nitride (Ni-SN@C) catalyst that is active and stable for the HER in alkaline seawater is prepared. It achieves a low overpotential of 23 mV at a current density of 10 mA cm −2 in alkaline seawater electrolyte, which is superior to Pt/C. Compared to conv...

Binary transition metal oxides (BTMOs) possess higher reversible capacity, better structural stability and electronic conductivity, and have been widely studied to be novel electrode materials for supercapacitors.

Present one-step N 2 fixation is impeded by tough activation of the NNb ond and low selectivity to NH 3 .H ere we report fixation of N 2 -to-NH 3 can be decoupled to atwo-step process with one problem effectively solved in each step, including:1)facile activation of N 2 to NO x À by anon-thermal plasma technique,a nd 2) highly selective conversion of NO x À to NH 3 by electrocatalytic reduction. Importantly,this process uses air and water as low-cost raw materials for scalable ammonia production under ambient conditions.F or NO x À reduction to NH 3 ,w ep resent as urface boron-richc ore-shell nickel boride electrocatalyst. The surface boron-rich feature is the key to boosting activity,s electivity,a nd stability via enhanced NO x À adsorption, and suppression of hydrogen evolution and surface Ni oxidation. As ignificant ammonia production of 198.3 mmol cm À2 h À1 was achieved, together with nearly 100 %F aradaic efficiency.