Robust covalent organic frameworks (COFs) with abundant redox-active sites have attracted intense attention for organic cathode materials due to the ordered structure and excellent stability. Herein, a two-dimensional (2D) crystalline copper-porphyrin covalent triazine framework (CuBCPP-CTF) was synthesized via polycondensation of 5,15-bis(4-cyanophenyl) porphyrin (H₂BCPP) and followed by post-copperization. The integration of copper-porphyrin moieties and triazine linkages provides two kinds of functional sites for outstanding Li⁺ and PF₆⁻ ions storage. Electrochemical studies reveal a high discharge capacity of 232 mAh·g⁻¹ at 200 mA·g⁻¹ and high mid-point voltage (2.77 V vs. Li⁺/Li), corresponding to an outstanding energy density of 601 Wh·kg⁻¹. Density functional theory calculations and ex-situ characterizations disclose the intrinsic bipolar redox mechanism of metalloporphyrin for both PF₆⁻ and Li⁺ accommodation and p-type triazine units for PF₆⁻ storage.

As a desirable alternative for oxygen evolution reaction (OER), urea oxidation reaction (UOR) with the effectively reduced overpotential has attracted considerable attention in pollutant degradation and rechargeable Zn-air battery (ZAB). Herein, a bifunctional electrocatalyst with CoNi alloy and CoN dual active sites encapsulated by nitrogen-doped carbon nanotubes have been rationally designed and successfully prepared. The as-obtained catalyst CoNi/Co–NCNT displays excellent catalytic activity for oxygen reduction (ORR) and UOR with a narrow potential difference of 0.56 V. The urea-assisted rechargeable ZABs based on CoNi/Co–NCNT provide higher energy conversion efficiency (61%), 15% higher than that of conventional ZABs. In addition to verify the UOR pathway on the CoNi/Co–NCNT, DFT calculations reveal that CoNi alloy and CoN in CoNi/Co–NCNT synergistically function as the main active sites for ORR and UOR. The excellent ORR catalytic performance and the superior energy conversion efficiency of CoNi/Co–NCNT based urea-assisted rechargeable ZAB is expected to accelerate the practical application of ZAB technology. This work paved a new way for the development of bifunctional catalysts for higher efficiency ZABs, and also provides a potential scheme for disposing urea rich wastewater.

Electrochemical CO₂ reduction is a viable, economical, and sustainable method to transform atmospheric CO₂ into carbon-based fuels and effectively reduce climate change and the energy crisis. Constructing robust catalysts through interface engineering is significant for electrocatalytic CO₂ reduction (ECR) but remains a grand challenge. Herein, SnO₂/Bi₂O₂CO₃ heterojunction on N,S-codoped-carbon (SnO₂/BOC@NSC) with efficient ECR performance was firstly constructed by a facile synthetic strategy. When the SnO₂/BOC@NSC was utilized in ECR, it exhibits a large formic acid (HCOOH) partial current density (J_HCOOH) of 86.7 mA·cm⁻² at −1.2 V versus reversible hydrogen electrode (RHE) and maximum Faradaic efficiency (FE) of HCOOH (90.75% at −1.2 V versus RHE), respectively. Notably, the FE_HCOOH of SnO₂/BOC@NSC is higher than 90% in the flow cell and the J_HCOOH of SnO₂/BOC@NSC can achieve 200 mA·cm⁻² at −0.8 V versus RHE to meet the requirements of industrialization level. The comparative experimental analysis and in-situ X-ray absorption fine structure reveal that the excellent ECR performance can be ascribed to the synergistic effect of SnO₂/BOC heterojunction, which enhances the activation of CO₂ molecules and improves electron transfer. This work provides an efficient SnO₂-based heterojunction catalyst for effective formate production and offers a novel approach for the construction of new types of metal oxide heterostructures for other catalytic applications.

It is vitally important to develop high-efficiency low-cost catalysts to boost oxygen reduction reaction (ORR) for renewable energy conversion. Herein, an A-CoN₃S₁@C electrocatalyst with atomic CoN₃S₁ active sites loaded on N, S-codoped porous carbon was produced by an atomic exchange strategy. The constructed A-CoN₃S₁@C electrocatalyst exhibits an unexpected half-wave potential (0.901 V vs. reversible hydrogen electrode) with excellent durability for ORR under alkaline conditions (0.1 M KOH), superior to the commercial platinum carbon (20 wt.% Pt/C). The outstanding performance of A-CoN₃S₁@C in ORR is due to the positive effect of S atoms doping on optimizing the electron structure of the atomic CoN₃S₁ active sites. Moreover, the rechargeable zinc-air battery in which both A-CoN₃S₁@C and IrO₂ were simultaneously served as cathode catalysts (A-CoN₃S₁@C &IrO ₂) exhibits higher energy efficiency, larger power density, as well as better stability, compared to the commercial Pt/C&IrO₂-based zinc-air battery. The present result should be helpful for developing lower cost and higher performance ORR catalysts which is expected to be used in practical applications in energy devices.