Electrocatalytic CO₂ reduction reaction (CRR) is considered as a sustainable approach to converting CO₂ into high value-added chemicals, assisting the goal of carbon peaking and carbon neutrality. Electrochemical CRR can be easily regulated by controlling the electrocatalyst, electrolyte, and reactor to produce various chemicals. Among different products, multi-carbon (C₂₊) products draw widespread attention for their high energy density and value along with complex reaction mechanisms. It is well recognized that *CO intermediate plays vital role in forming C₂₊ products and Cu is the only metal catalyst which can efficiently electro-reduce CO₂ to C₂₊ products. Therefore, researchers developed many strategies to increase the amount of *CO intermediate and further enhance the performance of C₂₊ products. Recently, designing tandem electrocatalysts consisted of Cu and the materials which can convert CO₂ to *CO intermediate has become a hotspot and achieved great achievements. In this review, we will summary the recent progress in tandem electrocatalysts for CO₂ reduction to prepare C₂₊ products, including the origin and fundamental mechanism of tandem electrocatalysis, the strategies of catalyst design, and regulation principles. In addition, some newest findings, like Cu tandem catalysts can achieve to produce C₂₊ products, are well introduced. Finally, the remaining challenges and prospects for future development are also proposed.

The commercialization of sodium-ion batteries is based on developing low-cost, highly stable, and safe cathode and anode electrodes. However, the promising hard carbon anode and layered oxide cathode suffer from low sodium-embedded potential near 0.1 V and severe phase transitions, which cause safe problem and short lifespan, respectively. Herein, we design a low-strain bipolar P2-Na_0.7Ni_0.25Fe_0.2Ti_0.55O₂ to solve the mentioned obstacles, whereas (Ni, Fe) and Ti provide charge compensation when it is used as cathode and anode, respectively. It is revealed that the bipolar layered oxide undergoes solid–solution reaction when used as cathode or anode, and exhibits volume-complementary feature in a sodium-ion full-cell, as identified by in-situ X-ray diffraction. Remarkably, the safe symmetric sodium-ion full-cell exhibits excellent cyclic stability with 91.7% capacity retention after 200 cycles. This work will provide a new horizon for designing safe and stable sodium-ion batteries.