Electronegative Phosphorus-Integrated Co2+ Active Sites for Enhanced Electrocatalytic Nitrogen Reduction.

In the quest for proficient electrocatalysts for ammonia's electrocatalytic nitrogen reduction, cobalt oxides, endowed with a rich d-electron reservoir, have emerged as frontrunners. Despite the previously evidenced prowess of CoO in this realm, its ammonia yield witnesses a pronounced decline as the reaction unfolds, a phenomenon linked to the electron attrition from its Co2+ active sites during electrocatalytic nitrogen reduction reaction (ENRR). To counteract this vulnerability, we harnessed electron-laden phosphorus (P) elements as dopants, aiming to recalibrate the electronic equilibrium of the pivotal Co active site, thereby bolstering both its catalytic performance and stability. Our empirical endeavors showcased the doped P-CoO's superior credentials: it delivered an impressive ammonia yield of 49.6 and, notably, a Faradaic efficiency (FE) of 9.6% at -0.2 V versus RHE, markedly eclipsing its undoped counterpart. Probing deeper, a suite of ex-situ techniques, complemented by rigorous theoretical evaluations, was deployed. This dual-pronged analysis unequivocally revealed CoO's propensity for an electron-driven valence metamorphosis to Co3+ post-ENRR. In stark contrast, P-CoO, fortified by P doping, exhibits a discernibly augmented ammonia yield. Crucially, P's intrinsic ability to staunch electron leakage from the active locus during ENRR ensures the preservation of the valence state, culminating in enhanced catalytic dynamism and fortitude. This investigation not only illuminates the intricacies of active site electronic modulation in ENRR but also charts a navigational beacon for further enhancements in this domain.

Built-in Electric Field-Induced Work Function Reduction in C-Co3O4 for Efficient Electrochemical Nitrogen Reduction.

Co3O4 is a highly selective catalyst for the electrochemical conversion of N2 to NH3. However, the large work function (WF) of Co3O4 leads to unsatisfactory activity. To address this issue, a strong built-in electric field (BIEF) was constructed in Co3O4 by doping C atoms (C-Co3O4) to reduce the WF for improving the electrocatalytic performance. C-Co3O4 exhibited a remarkable NH3 yield of 38.5 µg h-1 mgcat-1 and a promoted FE of 15.1% at -0.3 V vs RHE, which were 2.2 and 1.9 times higher than those of pure Co3O4, respectively. Kelvin probe force microscopy (KPFM), zeta potential, and ultraviolet photoelectron spectrometry (UPS) confirmed the formation of strong BIEF and WF reduction in C-Co3O4. Additionally, in situ Raman measurements and density functional theory (DFT) calculations revealed the relationship between BIEF and WF and provided insights into the reaction mechanism. Our work offers valuable guidance for the design and development of more efficient nitrogen reduction catalysts.

Regulation of the Work Function Difference Promotes In Situ Phase Transition of WO3-x for Efficient Formate Electrooxidation.

Direct formate fuel cells (DFFCs) have drawn tremendous attention because they are environmentally benign and have good safety. However, the lack of advanced catalysts for formate electrooxidation hinders the development and applications of DFFCs. Herein, we report a strategy of regulating the metal-substrate work function difference to effectively promote the transfer of adsorbed hydrogen (Had), thus enhancing formate electrooxidation in alkaline solutions. By introducing rich oxygen vacancies, the obtained catalysts of Pd/WO3-x-R show outstanding formate electrooxidation activity, exhibiting an extremely high peak current of 15.50 mA cm-2 with a lower peak potential of 0.63 V. In situ electrochemical Fourier transform infrared and in situ Raman measurements verify an enhanced in situ phase transition from WO3-x to HxWO3-x during the formate oxidation reaction process over the Pd/WO3-x-R catalyst. The results of experimental and density functional theory (DFT) calculations confirm that the work function difference (ΔΦ) between the metal (Pd) and substrate (WO3-x) would be regulated by inducing oxygen vacancies in the substrate, resulting in improved hydrogen spillover at the interface of the catalyst, which is essentially responsible for the observed high performance of formate oxidation. Our findings provide a novel strategy of rationally designing efficient formate electrooxidation catalysts.

Local Electric Field Induced by Atomic-Level Donor-Acceptor Couple of O Vacancies and Mn Atoms Enables Efficient Hybrid Capacitive Deionization.

Transition metal oxides suffer from slow salt removal rate (SRR) due to inferior ions diffusion ability in hybrid capacitive deionization (HCDI). Local electric field (LEF) can efficiently improve the ions diffusion kinetics in thin electrodes for electrochemical energy storage. Nevertheless, it is still a challenge to facilitate the ions diffusion in bulk electrodes with high loading mass for HCDI. Herein, this work delicately constructs a LEF via engineering atomic-level donor (O vacancies)-acceptor (Mn atoms) couples, which significantly facilitates the ions diffusion and then enables a high-performance HCDI. The LEF boosts an extended accelerated ions diffusion channel at the particle surface and interparticle space, resulting in both remarkably enhanced SRR and salt removal capacity. Convincingly, the theoretical calculations demonstrate that electron-enriched Mn atoms center coupled with an electron-depleted O vacancies center is formed due to the electron back-donation from O vacancies to adjacent Mn centers. The resulted LEF efficiently reduce the ions diffusion energy barrier. This work sheds light on the effect of atomic-level LEF on improving ions diffusion kinetics at high loading mass application and paves the way for the design of transition metal oxides toward high-performance HCDI applications.

Shearing Sulfur Edges of VS2 Electrocatalyst Enhances its Nitrogen Reduction Performance.

Electrochemical N2 fixation requires effective electrocatalysts to expedite the nitrogen reduction reaction (NRR) kinetics and suppress the concomitant hydrogen evolution reaction (HER). Although transition metal sulfides have been deemed as efficient NRR electrocatalysts, it remains a great challenge to suppress the serious HER to achieve high Faradaic efficiency (FE). Herein, vanadium disulfide (VS2 ) is deliberately designed by partially shearing its sulfur (S) edges through a simple calcination treatment at 350 °C. The as-prepared VS2 -350 electrocatalyst exhibits a highest NH3 yield of 20.29 µg h-1 mgcat-1 with a promising FE of 3.86%, which is significantly higher than the counterpart of untreated VS2 (VNH3 : 15.92 µg h-1 mgcat-1 , FE: 1.69%). Experimental and computational results reveal that shearing the S edges can substantially inhibit the HER and expose more V atoms as active sites. Meanwhile, the mechanistic analysis shows that the N2 activation at V active sites follows an "acceptance-donation" mechanism, while the N2 conversion to NH3 follows a hybrid 2 pathway at the VS2 -350 electrocatalyst. This work provides a simple strategy of designing high-performance NRR electrocatalysts based on a deep understanding of the atomic sites dependent catalytical activity.