As a profitable product from CO 2 electroreduction, HCOOH holds economic viability only when the selectivity is higher than 90% with current density (j) over −200.0 mA cm −2. Herein, Bi@Sn core-shell nanoparticles (Bi core and Sn shell, denoted as Bi@Sn NPs) are developed to boost the activity and selectivity of CO 2 electroreduction into HCOOH. In an H-cell system with 0.5 m KHCO 3 as electrolyte, Bi@Sn NPs exhibit a Faradaic efficiency for HCOOH (FE HCOOH) of 91% with partial j for HCOOH (j HCOOH) of −31.0 mA cm −2 at −1.1 V versus reversible hydrogen electrode. The potential application of Bi@Sn NPs is testified via chronopotentiometric measurements in the flow-cell system with 2.0 m KHCO 3 electrolyte. Under this circumstance, Bi@Sn NPs achieve an FE HCOOH of 92% with an energy efficiency of 56% at steady-state j of −250.0 mA cm −2. Theoretical studies indicate that the energy barrier of the potential-limiting step for the formation of HCOOH is decreased owing to the compressive strain in the Sn shell, resulting in the enhanced catalytic performance. The excessive utilization of fossil fuels and accelerating emissions of CO 2 have led to the energy shortage and greenhouse effect. [1-5] CO 2 electroreduction into useful chemicals and fuels represents a promising way that not only meets the everincreasing energy demands but also mitigates environmental crisis caused by CO 2 emissions. [6-11] As a value-added product from CO 2 electroreduction, formic acid (HCOOH) is an important feedstock for pharmaceutical and chemical industry. [12] Meanwhile, HCOOH is a liquid fuel for proton-exchange membrane

The functional status of innate immune cells is a considerable determinant of effective antitumor immune response. However, the triple-negative breast cancer tumor microenvironment with high lactic acid metabolism and high antioxidant levels limits immune cell survival, differentiation, and function. Here, we determine that the tumor microenvironment-responsive nano-ultrasonic contrast agent Pt­(IV)/CQ/PFH NPs-DPPA-1 boosts the ratio of mature dendritic cells (mDCs) and proinflammatory macrophages by reprogramming the metabolism of immature DCs (iDCs) and tumor-associated macrophages (TAMs). Specifically, platinum­(IV) in cancer cells or iDCs was reduced to cisplatin, which can increase the intracellular content of ROS and therefore enhance the ratio of mDCs and apoptotic tumor cells. Meanwhile, chloroquine (CQ) released from nanoparticles (NPs) minimizes protective autophagy caused by cisplatin in tumor cells and reprograms the metabolism of TAMs to enhance the proportion of proinflammatory macrophages, achieving a superior synergistic effect of chemoimmunotherapy combined with Pt­(IV) and anti-PD-L1 peptide (DPPA-1). Furthermore, perfluorohexane (PFH) in NPs realizes monitoring treatment corresponding to ultrasound. Collectively, the nano-ultrasonic contrast agent supports a candidate for monitoring treatment and augmenting antitumor chemoimmunotherapy by suppressing tumor cell autophagy and reprogramming immunocyte metabolism.